Mercurial > dropbear
diff libtommath/bn_mp_expt_u32.c @ 1692:1051e4eea25a
Update LibTomMath to 1.2.0 (#84)
* update C files
* update other files
* update headers
* update makefiles
* remove mp_set/get_double()
* use ltm 1.2.0 API
* update ltm_desc
* use bundled tommath if system-tommath is too old
* XMALLOC etc. were changed to MP_MALLOC etc.
| author | Steffen Jaeckel <s@jaeckel.eu> |
|---|---|
| date | Tue, 26 May 2020 17:36:47 +0200 |
| parents | |
| children |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/libtommath/bn_mp_expt_u32.c Tue May 26 17:36:47 2020 +0200 @@ -0,0 +1,46 @@ +#include "tommath_private.h" +#ifdef BN_MP_EXPT_U32_C +/* LibTomMath, multiple-precision integer library -- Tom St Denis */ +/* SPDX-License-Identifier: Unlicense */ + +/* calculate c = a**b using a square-multiply algorithm */ +mp_err mp_expt_u32(const mp_int *a, uint32_t b, mp_int *c) +{ + mp_err err; + + mp_int g; + + if ((err = mp_init_copy(&g, a)) != MP_OKAY) { + return err; + } + + /* set initial result */ + mp_set(c, 1uL); + + while (b > 0u) { + /* if the bit is set multiply */ + if ((b & 1u) != 0u) { + if ((err = mp_mul(c, &g, c)) != MP_OKAY) { + goto LBL_ERR; + } + } + + /* square */ + if (b > 1u) { + if ((err = mp_sqr(&g, &g)) != MP_OKAY) { + goto LBL_ERR; + } + } + + /* shift to next bit */ + b >>= 1; + } + + err = MP_OKAY; + +LBL_ERR: + mp_clear(&g); + return err; +} + +#endif