/* * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org> * * Permission is hereby granted, free of charge, to any person obtaining * a copy of this software and associated documentation files (the * "Software"), to deal in the Software without restriction, including * without limitation the rights to use, copy, modify, merge, publish, * distribute, sublicense, and/or sell copies of the Software, and to * permit persons to whom the Software is furnished to do so, subject to * the following conditions: * * The above copyright notice and this permission notice shall be * included in all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE * SOFTWARE. */ #include "inner.h" /* see inner.h */ uint32_t br_i32_decode_mod(uint32_t *x, const void *src, size_t len, const uint32_t *m) { const unsigned char *buf; uint32_t r; size_t u, v, mlen; buf = src; /* * First pass: determine whether the value fits. The 'r' value * will contain the comparison result, as 0x00000000 (value is * equal to the modulus), 0x00000001 (value is greater than the * modulus), or 0xFFFFFFFF (value is lower than the modulus). */ mlen = (m[0] + 7) >> 3; r = 0; for (u = (mlen > len) ? mlen : len; u > 0; u --) { uint32_t mb, xb; v = u - 1; if (v >= mlen) { mb = 0; } else { mb = (m[1 + (v >> 2)] >> ((v & 3) << 3)) & 0xFF; } if (v >= len) { xb = 0; } else { xb = buf[len - u]; } r = MUX(EQ(r, 0), (uint32_t)CMP(xb, mb), r); } /* * Only r == 0xFFFFFFFF is acceptable. We want to set r to 0xFF if * the value fits, 0x00 otherwise. */ r >>= 24; br_i32_zero(x, m[0]); u = (mlen > len) ? len : mlen; while (u > 0) { uint32_t xb; xb = buf[len - u] & r; u --; x[1 + (u >> 2)] |= xb << ((u & 3) << 3); } return r >> 7; } |