51 lines
1.3 KiB
C
51 lines
1.3 KiB
C
/* TomsFastMath, a fast ISO C bignum library.
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*
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* This project is meant to fill in where LibTomMath
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* falls short. That is speed ;-)
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*
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* This project is public domain and free for all purposes.
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*
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* Tom St Denis, tomstdenis@gmail.com
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*/
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#include "bignum_fast.h"
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/* c = a - b */
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void fp_sub(fp_int *a, fp_int *b, fp_int *c)
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{
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int sa, sb;
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sa = a->sign;
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sb = b->sign;
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if (sa != sb) {
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/* subtract a negative from a positive, OR */
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/* subtract a positive from a negative. */
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/* In either case, ADD their magnitudes, */
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/* and use the sign of the first number. */
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c->sign = sa;
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s_fp_add (a, b, c);
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} else {
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/* subtract a positive from a positive, OR */
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/* subtract a negative from a negative. */
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/* First, take the difference between their */
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/* magnitudes, then... */
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if (fp_cmp_mag (a, b) != FP_LT) {
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/* Copy the sign from the first */
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c->sign = sa;
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/* The first has a larger or equal magnitude */
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s_fp_sub (a, b, c);
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} else {
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/* The result has the *opposite* sign from */
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/* the first number. */
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c->sign = (sa == FP_ZPOS) ? FP_NEG : FP_ZPOS;
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/* The second has a larger magnitude */
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s_fp_sub (b, a, c);
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}
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}
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}
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/* $Source: /cvs/libtom/tomsfastmath/src/addsub/fp_sub.c,v $ */
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/* $Revision: 1.1 $ */
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/* $Date: 2006/12/31 21:25:53 $ */
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