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Diffstat (limited to 'libtommath/bn_mp_div_d.c')
-rw-r--r-- | libtommath/bn_mp_div_d.c | 110 |
1 files changed, 110 insertions, 0 deletions
diff --git a/libtommath/bn_mp_div_d.c b/libtommath/bn_mp_div_d.c new file mode 100644 index 0000000..7cb12f2 --- /dev/null +++ b/libtommath/bn_mp_div_d.c @@ -0,0 +1,110 @@ +#include <tommath.h> +#ifdef BN_MP_DIV_D_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@iahu.ca, http://math.libtomcrypt.org + */ + +static int s_is_power_of_two(mp_digit b, int *p) +{ + int x; + + for (x = 1; x < DIGIT_BIT; x++) { + if (b == (((mp_digit)1)<<x)) { + *p = x; + return 1; + } + } + return 0; +} + +/* single digit division (based on routine from MPI) */ +int mp_div_d (mp_int * a, mp_digit b, mp_int * c, mp_digit * d) +{ + mp_int q; + mp_word w; + mp_digit t; + int res, ix; + + /* cannot divide by zero */ + if (b == 0) { + return MP_VAL; + } + + /* quick outs */ + if (b == 1 || mp_iszero(a) == 1) { + if (d != NULL) { + *d = 0; + } + if (c != NULL) { + return mp_copy(a, c); + } + return MP_OKAY; + } + + /* power of two ? */ + if (s_is_power_of_two(b, &ix) == 1) { + if (d != NULL) { + *d = a->dp[0] & ((((mp_digit)1)<<ix) - 1); + } + if (c != NULL) { + return mp_div_2d(a, ix, c, NULL); + } + return MP_OKAY; + } + +#ifdef BN_MP_DIV_3_C + /* three? */ + if (b == 3) { + return mp_div_3(a, c, d); + } +#endif + + /* no easy answer [c'est la vie]. Just division */ + if ((res = mp_init_size(&q, a->used)) != MP_OKAY) { + return res; + } + + q.used = a->used; + q.sign = a->sign; + w = 0; + for (ix = a->used - 1; ix >= 0; ix--) { + w = (w << ((mp_word)DIGIT_BIT)) | ((mp_word)a->dp[ix]); + + if (w >= b) { + t = (mp_digit)(w / b); + w -= ((mp_word)t) * ((mp_word)b); + } else { + t = 0; + } + q.dp[ix] = (mp_digit)t; + } + + if (d != NULL) { + *d = (mp_digit)w; + } + + if (c != NULL) { + mp_clamp(&q); + mp_exch(&q, c); + } + mp_clear(&q); + + return res; +} + +#endif + +/* $Source: /root/tcl/repos-to-convert/tcl/libtommath/bn_mp_div_d.c,v $ */ +/* $Revision: 1.1.1.1.2.1 $ */ +/* $Date: 2005/09/26 20:16:53 $ */ |