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37 lines
651 B
C
37 lines
651 B
C
#ifdef __x86_64__
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/* WARNING: this only works if compiled with -fomit-frame-pointer */
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void imult64() {
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asm volatile(
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"xchgq %rdx,%rsi\n"
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"movq %rdi,%rax\n"
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"imulq %rdx\n"
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"jc 1f\n" /* overflow */
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"movq %rax,(%rsi)\n"
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"xorq %rax,%rax\n"
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"inc %rax\n"
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"ret\n"
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"1:\n"
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"xorq %rax,%rax\n"
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/* the closing ret is renerated by gcc */
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);
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}
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#else
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#include "safemult.h"
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int imult64(int64 a,int64 b,int64* c) {
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int neg=(a<0);
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uint64 d;
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if (neg) a=-a;
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if (b<0) { neg^=1; b=-b; }
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if (!umult64(a,b,&d)) return 0;
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if (d > 0x7fffffffffffffffULL + neg) return 0;
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*c=(neg?-d:d);
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return 1;
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}
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#endif
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