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integer.c: refactoring mp_exptmod_fast to reduce stack usage:

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--- variable M moved to the heap (512 bytes saved)
This commit is contained in:
Moisés Guimarães
2015-05-28 17:11:29 -03:00
parent a7a00a4bd5
commit ed65565390
1 changed files with 27 additions and 2 deletions
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29
wolfcrypt/src/integer.c
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@@ -1721,16 +1721,27 @@ int mp_dr_is_modulus(mp_int *a)
int mp_exptmod_fast (mp_int * G, mp_int * X, mp_int * P, mp_int * Y, int mp_exptmod_fast (mp_int * G, mp_int * X, mp_int * P, mp_int * Y,
int redmode) int redmode)
{ {
mp_int M[TAB_SIZE], res; mp_int res;
mp_digit buf, mp; mp_digit buf, mp;
int err, bitbuf, bitcpy, bitcnt, mode, digidx, x, y, winsize; int err, bitbuf, bitcpy, bitcnt, mode, digidx, x, y, winsize;
#ifdef WOLFSSL_SMALL_STACK
mp_int* M = NULL;
#else
mp_int M[TAB_SIZE];
#endif
/* use a pointer to the reduction algorithm. This allows us to use /* use a pointer to the reduction algorithm. This allows us to use
* one of many reduction algorithms without modding the guts of * one of many reduction algorithms without modding the guts of
* the code with if statements everywhere. * the code with if statements everywhere.
*/ */
int (*redux)(mp_int*,mp_int*,mp_digit); int (*redux)(mp_int*,mp_int*,mp_digit);
#ifdef WOLFSSL_SMALL_STACK
M = (mp_int*) XMALLOC(sizeof(mp_int) * TAB_SIZE, NULL,
DYNAMIC_TYPE_TMP_BUFFER);
if (M == NULL)
return MP_MEM;
#endif
/* find window size */ /* find window size */
x = mp_count_bits (X); x = mp_count_bits (X);
if (x <= 7) { if (x <= 7) {
@@ -1758,6 +1769,10 @@ int mp_exptmod_fast (mp_int * G, mp_int * X, mp_int * P, mp_int * Y,
/* init M array */ /* init M array */
/* init first cell */ /* init first cell */
if ((err = mp_init(&M[1])) != MP_OKAY) { if ((err = mp_init(&M[1])) != MP_OKAY) {
#ifdef WOLFSSL_SMALL_STACK
XFREE(M, NULL, DYNAMIC_TYPE_TMP_BUFFER);
#endif
return err; return err;
} }
@@ -1768,6 +1783,11 @@ int mp_exptmod_fast (mp_int * G, mp_int * X, mp_int * P, mp_int * Y,
mp_clear (&M[y]); mp_clear (&M[y]);
} }
mp_clear(&M[1]); mp_clear(&M[1]);
#ifdef WOLFSSL_SMALL_STACK
XFREE(M, NULL, DYNAMIC_TYPE_TMP_BUFFER);
#endif
return err; return err;
} }
} }
@@ -2002,6 +2022,11 @@ LBL_M:
for (x = 1<<(winsize-1); x < (1 << winsize); x++) { for (x = 1<<(winsize-1); x < (1 << winsize); x++) {
mp_clear (&M[x]); mp_clear (&M[x]);
} }
#ifdef WOLFSSL_SMALL_STACK
XFREE(M, NULL, DYNAMIC_TYPE_TMP_BUFFER);
#endif
return err; return err;
} }