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421
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1 /* alloca.c -- allocate automatically reclaimed memory
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2 (Mostly) portable public-domain implementation -- D A Gwyn
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3
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4 This implementation of the PWB library alloca function,
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5 which is used to allocate space off the run-time stack so
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6 that it is automatically reclaimed upon procedure exit,
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7 was inspired by discussions with J. Q. Johnson of Cornell.
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8 J.Otto Tennant <jot@cray.com> contributed the Cray support.
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9
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10 There are some preprocessor constants that can
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11 be defined when compiling for your specific system, for
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12 improved efficiency; however, the defaults should be okay.
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13
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14 The general concept of this implementation is to keep
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15 track of all alloca-allocated blocks, and reclaim any
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16 that are found to be deeper in the stack than the current
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17 invocation. This heuristic does not reclaim storage as
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18 soon as it becomes invalid, but it will do so eventually.
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19
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20 As a special case, alloca(0) reclaims storage without
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21 allocating any. It is a good idea to use alloca(0) in
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22 your main control loop, etc. to force garbage collection. */
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23
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24 #include <config.h>
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25
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26 #include <alloca.h>
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27
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28 #include <string.h>
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29 #include <stdlib.h>
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30
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31 #ifdef emacs
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32 # include "lisp.h"
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33 # include "blockinput.h"
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34 # ifdef EMACS_FREE
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35 # undef free
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36 # define free EMACS_FREE
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37 # endif
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38 #else
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39 # define memory_full() abort ()
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40 #endif
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41
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42 /* If compiling with GCC 2, this file's not needed. */
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43 #if !defined (__GNUC__) || __GNUC__ < 2
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44
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45 /* If someone has defined alloca as a macro,
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46 there must be some other way alloca is supposed to work. */
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47 # ifndef alloca
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48
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49 # ifdef emacs
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50 # ifdef static
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51 /* actually, only want this if static is defined as ""
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52 -- this is for usg, in which emacs must undefine static
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53 in order to make unexec workable
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54 */
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55 # ifndef STACK_DIRECTION
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56 you
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57 lose
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58 -- must know STACK_DIRECTION at compile-time
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59 /* Using #error here is not wise since this file should work for
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60 old and obscure compilers. */
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61 # endif /* STACK_DIRECTION undefined */
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62 # endif /* static */
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63 # endif /* emacs */
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64
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65 /* If your stack is a linked list of frames, you have to
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66 provide an "address metric" ADDRESS_FUNCTION macro. */
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67
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68 # if defined (CRAY) && defined (CRAY_STACKSEG_END)
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69 long i00afunc ();
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70 # define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
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71 # else
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72 # define ADDRESS_FUNCTION(arg) &(arg)
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73 # endif
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74
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75 /* Define STACK_DIRECTION if you know the direction of stack
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76 growth for your system; otherwise it will be automatically
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77 deduced at run-time.
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78
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79 STACK_DIRECTION > 0 => grows toward higher addresses
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80 STACK_DIRECTION < 0 => grows toward lower addresses
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81 STACK_DIRECTION = 0 => direction of growth unknown */
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82
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83 # ifndef STACK_DIRECTION
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84 # define STACK_DIRECTION 0 /* Direction unknown. */
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85 # endif
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86
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87 # if STACK_DIRECTION != 0
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88
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89 # define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
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90
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91 # else /* STACK_DIRECTION == 0; need run-time code. */
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92
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93 static int stack_dir; /* 1 or -1 once known. */
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94 # define STACK_DIR stack_dir
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95
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96 static void
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97 find_stack_direction (void)
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98 {
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99 static char *addr = NULL; /* Address of first `dummy', once known. */
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100 auto char dummy; /* To get stack address. */
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101
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102 if (addr == NULL)
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103 { /* Initial entry. */
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104 addr = ADDRESS_FUNCTION (dummy);
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105
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106 find_stack_direction (); /* Recurse once. */
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107 }
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108 else
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109 {
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110 /* Second entry. */
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111 if (ADDRESS_FUNCTION (dummy) > addr)
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112 stack_dir = 1; /* Stack grew upward. */
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113 else
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114 stack_dir = -1; /* Stack grew downward. */
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115 }
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116 }
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117
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118 # endif /* STACK_DIRECTION == 0 */
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119
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120 /* An "alloca header" is used to:
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121 (a) chain together all alloca'ed blocks;
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122 (b) keep track of stack depth.
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123
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124 It is very important that sizeof(header) agree with malloc
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125 alignment chunk size. The following default should work okay. */
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126
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127 # ifndef ALIGN_SIZE
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128 # define ALIGN_SIZE sizeof(double)
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129 # endif
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130
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131 typedef union hdr
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132 {
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133 char align[ALIGN_SIZE]; /* To force sizeof(header). */
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134 struct
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135 {
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136 union hdr *next; /* For chaining headers. */
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137 char *deep; /* For stack depth measure. */
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138 } h;
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139 } header;
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140
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141 static header *last_alloca_header = NULL; /* -> last alloca header. */
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142
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143 /* Return a pointer to at least SIZE bytes of storage,
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144 which will be automatically reclaimed upon exit from
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145 the procedure that called alloca. Originally, this space
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146 was supposed to be taken from the current stack frame of the
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147 caller, but that method cannot be made to work for some
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148 implementations of C, for example under Gould's UTX/32. */
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149
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150 void *
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151 alloca (size_t size)
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152 {
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153 auto char probe; /* Probes stack depth: */
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154 register char *depth = ADDRESS_FUNCTION (probe);
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155
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156 # if STACK_DIRECTION == 0
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157 if (STACK_DIR == 0) /* Unknown growth direction. */
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158 find_stack_direction ();
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159 # endif
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160
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161 /* Reclaim garbage, defined as all alloca'd storage that
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162 was allocated from deeper in the stack than currently. */
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163
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164 {
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165 register header *hp; /* Traverses linked list. */
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166
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167 # ifdef emacs
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168 BLOCK_INPUT;
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169 # endif
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170
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171 for (hp = last_alloca_header; hp != NULL;)
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172 if ((STACK_DIR > 0 && hp->h.deep > depth)
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173 || (STACK_DIR < 0 && hp->h.deep < depth))
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174 {
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175 register header *np = hp->h.next;
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176
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177 free (hp); /* Collect garbage. */
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178
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179 hp = np; /* -> next header. */
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180 }
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181 else
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182 break; /* Rest are not deeper. */
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183
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184 last_alloca_header = hp; /* -> last valid storage. */
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185
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186 # ifdef emacs
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187 UNBLOCK_INPUT;
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188 # endif
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189 }
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190
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191 if (size == 0)
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192 return NULL; /* No allocation required. */
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193
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194 /* Allocate combined header + user data storage. */
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195
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196 {
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197 /* Address of header. */
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198 register header *new;
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199
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200 size_t combined_size = sizeof (header) + size;
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201 if (combined_size < sizeof (header))
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202 memory_full ();
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203
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204 new = malloc (combined_size);
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205
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206 if (! new)
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207 memory_full ();
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208
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209 new->h.next = last_alloca_header;
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210 new->h.deep = depth;
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211
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212 last_alloca_header = new;
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213
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214 /* User storage begins just after header. */
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215
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216 return (void *) (new + 1);
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217 }
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218 }
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219
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220 # if defined (CRAY) && defined (CRAY_STACKSEG_END)
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221
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222 # ifdef DEBUG_I00AFUNC
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223 # include <stdio.h>
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224 # endif
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225
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226 # ifndef CRAY_STACK
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227 # define CRAY_STACK
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228 # ifndef CRAY2
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229 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
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230 struct stack_control_header
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231 {
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232 long shgrow:32; /* Number of times stack has grown. */
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233 long shaseg:32; /* Size of increments to stack. */
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234 long shhwm:32; /* High water mark of stack. */
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235 long shsize:32; /* Current size of stack (all segments). */
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236 };
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237
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238 /* The stack segment linkage control information occurs at
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239 the high-address end of a stack segment. (The stack
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240 grows from low addresses to high addresses.) The initial
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241 part of the stack segment linkage control information is
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242 0200 (octal) words. This provides for register storage
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243 for the routine which overflows the stack. */
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244
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245 struct stack_segment_linkage
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246 {
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247 long ss[0200]; /* 0200 overflow words. */
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248 long sssize:32; /* Number of words in this segment. */
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249 long ssbase:32; /* Offset to stack base. */
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250 long:32;
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251 long sspseg:32; /* Offset to linkage control of previous
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252 segment of stack. */
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253 long:32;
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254 long sstcpt:32; /* Pointer to task common address block. */
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255 long sscsnm; /* Private control structure number for
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256 microtasking. */
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257 long ssusr1; /* Reserved for user. */
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258 long ssusr2; /* Reserved for user. */
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259 long sstpid; /* Process ID for pid based multi-tasking. */
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260 long ssgvup; /* Pointer to multitasking thread giveup. */
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261 long sscray[7]; /* Reserved for Cray Research. */
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262 long ssa0;
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263 long ssa1;
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264 long ssa2;
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265 long ssa3;
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266 long ssa4;
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267 long ssa5;
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268 long ssa6;
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269 long ssa7;
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270 long sss0;
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271 long sss1;
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272 long sss2;
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273 long sss3;
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274 long sss4;
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275 long sss5;
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276 long sss6;
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277 long sss7;
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278 };
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279
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280 # else /* CRAY2 */
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281 /* The following structure defines the vector of words
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282 returned by the STKSTAT library routine. */
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283 struct stk_stat
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284 {
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285 long now; /* Current total stack size. */
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286 long maxc; /* Amount of contiguous space which would
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287 be required to satisfy the maximum
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288 stack demand to date. */
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289 long high_water; /* Stack high-water mark. */
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290 long overflows; /* Number of stack overflow ($STKOFEN) calls. */
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291 long hits; /* Number of internal buffer hits. */
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292 long extends; /* Number of block extensions. */
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293 long stko_mallocs; /* Block allocations by $STKOFEN. */
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294 long underflows; /* Number of stack underflow calls ($STKRETN). */
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295 long stko_free; /* Number of deallocations by $STKRETN. */
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296 long stkm_free; /* Number of deallocations by $STKMRET. */
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297 long segments; /* Current number of stack segments. */
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298 long maxs; /* Maximum number of stack segments so far. */
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299 long pad_size; /* Stack pad size. */
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300 long current_address; /* Current stack segment address. */
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301 long current_size; /* Current stack segment size. This
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302 number is actually corrupted by STKSTAT to
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303 include the fifteen word trailer area. */
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304 long initial_address; /* Address of initial segment. */
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305 long initial_size; /* Size of initial segment. */
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306 };
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307
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308 /* The following structure describes the data structure which trails
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309 any stack segment. I think that the description in 'asdef' is
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310 out of date. I only describe the parts that I am sure about. */
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311
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312 struct stk_trailer
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313 {
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314 long this_address; /* Address of this block. */
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315 long this_size; /* Size of this block (does not include
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316 this trailer). */
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317 long unknown2;
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318 long unknown3;
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319 long link; /* Address of trailer block of previous
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320 segment. */
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321 long unknown5;
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322 long unknown6;
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323 long unknown7;
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324 long unknown8;
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325 long unknown9;
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326 long unknown10;
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327 long unknown11;
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328 long unknown12;
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329 long unknown13;
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330 long unknown14;
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331 };
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332
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333 # endif /* CRAY2 */
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334 # endif /* not CRAY_STACK */
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335
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336 # ifdef CRAY2
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337 /* Determine a "stack measure" for an arbitrary ADDRESS.
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338 I doubt that "lint" will like this much. */
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339
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340 static long
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341 i00afunc (long *address)
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342 {
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343 struct stk_stat status;
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344 struct stk_trailer *trailer;
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345 long *block, size;
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346 long result = 0;
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347
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348 /* We want to iterate through all of the segments. The first
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349 step is to get the stack status structure. We could do this
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350 more quickly and more directly, perhaps, by referencing the
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351 $LM00 common block, but I know that this works. */
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352
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353 STKSTAT (&status);
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354
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355 /* Set up the iteration. */
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356
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357 trailer = (struct stk_trailer *) (status.current_address
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358 + status.current_size
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359 - 15);
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360
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361 /* There must be at least one stack segment. Therefore it is
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362 a fatal error if "trailer" is null. */
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363
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364 if (trailer == 0)
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365 abort ();
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366
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367 /* Discard segments that do not contain our argument address. */
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368
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369 while (trailer != 0)
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370 {
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371 block = (long *) trailer->this_address;
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372 size = trailer->this_size;
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373 if (block == 0 || size == 0)
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374 abort ();
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375 trailer = (struct stk_trailer *) trailer->link;
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376 if ((block <= address) && (address < (block + size)))
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377 break;
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378 }
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379
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380 /* Set the result to the offset in this segment and add the sizes
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381 of all predecessor segments. */
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382
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383 result = address - block;
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384
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385 if (trailer == 0)
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386 {
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387 return result;
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388 }
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389
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390 do
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391 {
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392 if (trailer->this_size <= 0)
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393 abort ();
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394 result += trailer->this_size;
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395 trailer = (struct stk_trailer *) trailer->link;
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396 }
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397 while (trailer != 0);
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398
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399 /* We are done. Note that if you present a bogus address (one
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400 not in any segment), you will get a different number back, formed
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401 from subtracting the address of the first block. This is probably
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402 not what you want. */
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403
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404 return (result);
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405 }
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406
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407 # else /* not CRAY2 */
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408 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
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409 Determine the number of the cell within the stack,
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410 given the address of the cell. The purpose of this
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411 routine is to linearize, in some sense, stack addresses
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412 for alloca. */
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413
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414 static long
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415 i00afunc (long address)
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416 {
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417 long stkl = 0;
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418
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419 long size, pseg, this_segment, stack;
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420 long result = 0;
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421
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422 struct stack_segment_linkage *ssptr;
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423
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424 /* Register B67 contains the address of the end of the
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425 current stack segment. If you (as a subprogram) store
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426 your registers on the stack and find that you are past
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427 the contents of B67, you have overflowed the segment.
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428
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429 B67 also points to the stack segment linkage control
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430 area, which is what we are really interested in. */
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431
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432 stkl = CRAY_STACKSEG_END ();
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433 ssptr = (struct stack_segment_linkage *) stkl;
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434
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435 /* If one subtracts 'size' from the end of the segment,
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436 one has the address of the first word of the segment.
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437
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438 If this is not the first segment, 'pseg' will be
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439 nonzero. */
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440
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441 pseg = ssptr->sspseg;
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442 size = ssptr->sssize;
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443
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444 this_segment = stkl - size;
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445
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446 /* It is possible that calling this routine itself caused
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447 a stack overflow. Discard stack segments which do not
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448 contain the target address. */
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449
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450 while (!(this_segment <= address && address <= stkl))
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451 {
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452 # ifdef DEBUG_I00AFUNC
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453 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
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454 # endif
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455 if (pseg == 0)
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456 break;
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457 stkl = stkl - pseg;
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458 ssptr = (struct stack_segment_linkage *) stkl;
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459 size = ssptr->sssize;
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460 pseg = ssptr->sspseg;
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461 this_segment = stkl - size;
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462 }
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463
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464 result = address - this_segment;
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465
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466 /* If you subtract pseg from the current end of the stack,
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467 you get the address of the previous stack segment's end.
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468 This seems a little convoluted to me, but I'll bet you save
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469 a cycle somewhere. */
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470
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471 while (pseg != 0)
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472 {
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473 # ifdef DEBUG_I00AFUNC
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474 fprintf (stderr, "%011o %011o\n", pseg, size);
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475 # endif
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476 stkl = stkl - pseg;
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477 ssptr = (struct stack_segment_linkage *) stkl;
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478 size = ssptr->sssize;
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479 pseg = ssptr->sspseg;
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480 result += size;
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481 }
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482 return (result);
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483 }
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484
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485 # endif /* not CRAY2 */
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486 # endif /* CRAY */
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487
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488 # endif /* no alloca */
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489 #endif /* not GCC version 3 */
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