144 lines
3.3 KiB
C
144 lines
3.3 KiB
C
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/* Copyright (c) 2005-2007 Apple Inc. All Rights Reserved. */
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/*
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* giantPort_C.h - Generic giant definitions routines, used when
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* no platform-specific version is available.
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*
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* This module works on any size giantDigit up to and including
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* the native unsigned int, as long as the platform does indeed
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* supply a (2 x giantDigit) unsigned integer, defined (in
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* giantPlatform.h) as a giantDouble.
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*
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* Created Aug. 8 2005 by Doug Mitchell.
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*/
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#include <libGiants/giantTypes.h>
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#include <libGiants/giantIntegers.h>
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#include <libGiants/giantPortCommon.h>
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#include <libGiants/giantDebug.h>
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#ifndef GI_GIANT_PORT_INLINE
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#error Please define GI_GIANT_PORT_INLINE.
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#endif
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#if !GI_GIANT_PORT_INLINE
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/*
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* Add two digits, return sum. Carry bit returned as an out parameter.
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*/
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giantDigit giantAddDigits(
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giantDigit dig1,
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giantDigit dig2,
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giantDigit *carry) /* RETURNED, 0 or 1 */
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{
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giantDigit sum = dig1 + dig2;
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GI_CHECK_SP("giantAddDigits");
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if((sum < dig1) || (sum < dig2)) {
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*carry = 1;
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}
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else {
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*carry = 0;
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}
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return sum;
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}
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/*
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* Add a single digit value to a double digit accumulator in place.
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* Carry out of the MSD of the accumulator is not handled.
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*/
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void giantAddDouble(
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giantDigit *accLow, /* IN/OUT */
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giantDigit *accHigh, /* IN/OUT */
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giantDigit val)
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{
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giantDigit sumLo = *accLow + val;
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GI_CHECK_SP("giantAddDouble");
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if((sumLo < *accLow) || (sumLo < val)) {
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(*accHigh)++;
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/* if it's zero we just overflowed */
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GIASSERT(*accHigh != 0);
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}
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*accLow = sumLo;
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}
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/*
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* Subtract a - b, return difference. Borrow bit returned as an out parameter.
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*/
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giantDigit giantSubDigits(
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giantDigit a,
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giantDigit b,
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giantDigit *borrow) /* RETURNED, 0 or 1 */
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{
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giantDigit diff = a - b;
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GI_CHECK_SP("giantSubDigits");
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if(a < b) {
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*borrow = 1;
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}
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else {
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*borrow = 0;
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}
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return diff;
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}
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/*
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* Multiply two digits, return two digits.
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*/
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void giantMulDigits(
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giantDigit dig1,
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giantDigit dig2,
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giantDigit *lowProduct, /* RETURNED, low digit */
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giantDigit *hiProduct) /* RETURNED, high digit */
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{
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giantDouble dprod;
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GI_CHECK_SP("giantMulDigits");
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dprod = (giantDouble)dig1 * (giantDouble)dig2;
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*hiProduct = (giantDigit)(dprod >> GIANT_BITS_PER_DIGIT);
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*lowProduct = (giantDigit)dprod;
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}
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#if 0
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/* this is currently unused. */
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/*
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* Multiply a vector of giantDigits, candVector, by a single giantDigit,
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* plierDigit, adding results into prodVector. Returns m.s. digit from
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* final multiply; only candLength digits of *prodVector will be written.
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*/
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giantDigit VectorMultiply(
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giantDigit plierDigit,
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giantDigit *candVector,
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gi_size candLength,
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giantDigit *prodVector)
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{
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gi_size candDex; // index into multiplicandVector
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giantDigit lastCarry = 0;
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giantDigit prodLo;
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giantDigit prodHi;
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for(candDex=0; candDex<candLength; ++candDex) {
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/*
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* prod = *(candVector++) * plierDigit + *prodVector + lastCarry
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*/
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giantMulDigits(*(candVector++),
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plierDigit,
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&prodLo,
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&prodHi);
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giantAddDouble(&prodLo, &prodHi, *prodVector);
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giantAddDouble(&prodLo, &prodHi, lastCarry);
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/*
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* *(destptr++) = prodHi;
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* lastCarry = prodLo;
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*/
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*(prodVector++) = prodLo;
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lastCarry = prodHi;
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}
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return lastCarry;
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}
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#endif /* 0 - VectorMultiply disabled */
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#endif /* !GI_GIANT_PORT_INLINE */
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