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23 lines
514 B
C
23 lines
514 B
C
22 years ago
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#include "safemult.h"
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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 1;
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a=(uint64)(ahi)*blo+(uint64)(alo)*bhi;
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if (a>0xffffffff) return 1;
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*c=(a<<32)+(uint64)(alo)*blo;
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return 0;
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}
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