c3-lang/libtommath/mp_mod_2d.c
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Hash : 795cd201
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Date : 2019-10-29T21:48:50
simplifications: add s_mp_zero_(digs|buf) and s_mp_copy_digs Originally I made those as macros. However we have many other small functions like mp_clamp, mp_exch which are also not implemented as macros right now. If we would use c99, I would implement them as private static inline functions. And mp_exch would be a public static inline function. But since we are bound to c89, we simply use normal functions. To achieve optimal performance one should either use link time optimization or amalgamation.
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mp_mod_2d.c
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#include "tommath_private.h" #ifdef MP_MOD_2D_C /* LibTomMath, multiple-precision integer library -- Tom St Denis */ /* SPDX-License-Identifier: Unlicense */ /* calc a value mod 2**b */ mp_err mp_mod_2d(const mp_int *a, int b, mp_int *c) { int x; mp_err err; if (b < 0) { return MP_VAL; } if (b == 0) { mp_zero(c); return MP_OKAY; } /* if the modulus is larger than the value than return */ if (b >= (a->used * MP_DIGIT_BIT)) { return mp_copy(a, c); } if ((err = mp_copy(a, c)) != MP_OKAY) { return err; } /* zero digits above the last digit of the modulus */ x = (b / MP_DIGIT_BIT) + (((b % MP_DIGIT_BIT) == 0) ? 0 : 1); s_mp_zero_digs(c->dp + x, c->used - x); /* clear the digit that is not completely outside/inside the modulus */ c->dp[b / MP_DIGIT_BIT] &= ((mp_digit)1 << (mp_digit)(b % MP_DIGIT_BIT)) - (mp_digit)1; mp_clamp(c); return MP_OKAY; } #endif