diff options
Diffstat (limited to 'libtommath/bn_mp_lshd.c')
-rw-r--r-- | libtommath/bn_mp_lshd.c | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/libtommath/bn_mp_lshd.c b/libtommath/bn_mp_lshd.c new file mode 100644 index 0000000..ce1e63b --- /dev/null +++ b/libtommath/bn_mp_lshd.c @@ -0,0 +1,63 @@ +#include <tommath.h> +#ifdef BN_MP_LSHD_C +/* LibTomMath, multiple-precision integer library -- Tom St Denis + * + * LibTomMath is a library that provides multiple-precision + * integer arithmetic as well as number theoretic functionality. + * + * The library was designed directly after the MPI library by + * Michael Fromberger but has been written from scratch with + * additional optimizations in place. + * + * The library is free for all purposes without any express + * guarantee it works. + * + * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com + */ + +/* shift left a certain amount of digits */ +int mp_lshd (mp_int * a, int b) +{ + int x, res; + + /* if its less than zero return */ + if (b <= 0) { + return MP_OKAY; + } + + /* grow to fit the new digits */ + if (a->alloc < a->used + b) { + if ((res = mp_grow (a, a->used + b)) != MP_OKAY) { + return res; + } + } + + { + register mp_digit *top, *bottom; + + /* increment the used by the shift amount then copy upwards */ + a->used += b; + + /* top */ + top = a->dp + a->used - 1; + + /* base */ + bottom = a->dp + a->used - 1 - b; + + /* much like mp_rshd this is implemented using a sliding window + * except the window goes the otherway around. Copying from + * the bottom to the top. see bn_mp_rshd.c for more info. + */ + for (x = a->used - 1; x >= b; x--) { + *top-- = *bottom--; + } + + /* zero the lower digits */ + top = a->dp; + for (x = 0; x < b; x++) { + *top++ = 0; + } + } + return MP_OKAY; +} +#endif |