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add POSITIVE_EXP_ONLY for fastmath stack reduction when positive exponents only

pull/1/head
toddouska 2013-05-23 15:55:22 -07:00
parent 8df0e43384
commit 8b90414f2a
1 changed files with 9 additions and 5 deletions
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14
ctaocrypt/src/tfm.c
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@ -1183,16 +1183,16 @@ static int _fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
int fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y) int fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
{ {
fp_int tmp;
int err;
/* prevent overflows */ /* prevent overflows */
if (P->used > (FP_SIZE/2)) { if (P->used > (FP_SIZE/2)) {
return FP_VAL; return FP_VAL;
} }
/* is X negative? */
if (X->sign == FP_NEG) { if (X->sign == FP_NEG) {
#ifndef POSITIVE_EXP_ONLY /* reduce stack if assume no negatives */
int err;
fp_int tmp;
/* yes, copy G and invmod it */ /* yes, copy G and invmod it */
fp_copy(G, &tmp); fp_copy(G, &tmp);
if ((err = fp_invmod(&tmp, P, &tmp)) != FP_OKAY) { if ((err = fp_invmod(&tmp, P, &tmp)) != FP_OKAY) {
@ -1204,7 +1204,11 @@ int fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
X->sign = FP_NEG; X->sign = FP_NEG;
} }
return err; return err;
} else { #else
return FP_VAL;
#endif
}
else {
/* Positive exponent so just exptmod */ /* Positive exponent so just exptmod */
return _fp_exptmod(G, X, P, Y); return _fp_exptmod(G, X, P, Y);
} }