63 lines
1.3 KiB
C
63 lines
1.3 KiB
C
#include <stdlib.h>
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#include <stdbool.h>
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#include <ctype.h>
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#include <errno.h>
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unsigned long long int strtoull(char const * restrict ptr,
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char ** restrict endptr, int base)
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{
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/* Save the value of ptr in endptr now in case the format is invalid */
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if(endptr) *endptr = (char *)ptr;
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/* Skip initial whitespace */
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while(isspace(*ptr)) ptr++;
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/* Accept a sign character */
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bool negative = false;
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if(*ptr == '-') negative = true;
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if(*ptr == '-' || *ptr == '+') ptr++;
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unsigned long long x = 0;
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bool valid = false;
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/* Read prefixes and determine base */
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if((base == 0 || base == 16) && ptr[0]=='0' && tolower(ptr[1])=='x') {
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ptr += 2;
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base = 16;
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}
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else if(base == 0 && ptr[0] == '0') {
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ptr++;
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base = 8;
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}
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else if(base == 0) {
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base = 10;
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}
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/* Read digits */
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while(1) {
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int v = -1;
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if(isdigit(*ptr)) v = *ptr - '0';
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if(islower(*ptr)) v = *ptr - 'a' + 10;
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if(v == -1 || v >= base) break;
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/* The value is valid as long as there is at least one digit */
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valid = true;
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/* (x = base*x + v) but with overflow checks */
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if(__builtin_umulll_overflow(x, base, &x))
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errno = ERANGE;
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if(__builtin_uaddll_overflow(x, v, &x))
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errno = ERANGE;
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ptr++;
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}
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if(negative) {
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if(x != 0) errno = ERANGE;
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x = -x;
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}
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if(endptr && valid) *endptr = (char *)ptr;
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return x;
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}
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