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60 lines
1.3 KiB
60 lines
1.3 KiB
#if defined(__x86_64__) && defined(__OPTIMIZE__) |
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/* WARNING: this only works if compiled with -fomit-frame-pointer */ |
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void umult64() { |
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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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"mulq %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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#if defined(__GNUC__) && (defined(__x86_64__) || defined(__ia64__) || defined(__powerpc64__) || defined(__alpha__) || defined(__mips64__) || defined(__sparc64__)) |
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int umult64(uint64 a,uint64 b,uint64* c) { |
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__uint128_t x=((__uint128_t)a)*b; |
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if ((*c=(uint64)x) != x) return 0; |
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return 1; |
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} |
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#else |
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/* return 1 for overflow, 0 for ok */ |
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int umult64(uint64 a,uint64 b,uint64* c) { |
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uint32 ahi=a>>32; |
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uint32 alo=(a&0xffffffff); |
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uint32 bhi=b>>32; |
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uint32 blo=(b&0xffffffff); |
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// a=ahi*x+alo, b=bhi*x+blo |
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// a*b = (ahi*x+alo) * (bhi*x+blo) |
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// = ahi*x*bhi*x + ahi*x*blo + alo*bhi*x + alo*blo |
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// -> overflow if ahi*bhi != zero */ |
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if (ahi && bhi) return 0; |
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a=(uint64)(ahi)*blo+(uint64)(alo)*bhi; |
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if (a>0xffffffff) return 0; |
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{ |
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uint64 x=(uint64)(alo)*blo; |
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if (x+(a<<32) < x) return 0; |
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*c=x+(a<<32); |
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} |
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return 1; |
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} |
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#endif |
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#endif
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