1 /* 2 * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org> 3 * 4 * Permission is hereby granted, free of charge, to any person obtaining 5 * a copy of this software and associated documentation files (the 6 * "Software"), to deal in the Software without restriction, including 7 * without limitation the rights to use, copy, modify, merge, publish, 8 * distribute, sublicense, and/or sell copies of the Software, and to 9 * permit persons to whom the Software is furnished to do so, subject to 10 * the following conditions: 11 * 12 * The above copyright notice and this permission notice shall be 13 * included in all copies or substantial portions of the Software. 14 * 15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 16 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 17 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 18 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS 19 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN 20 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN 21 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 22 * SOFTWARE. 23 */ 24 25 #include "inner.h" 26 27 /* see inner.h */ 28 uint32_t 29 br_i32_decode_mod(uint32_t *x, const void *src, size_t len, const uint32_t *m) 30 { 31 const unsigned char *buf; 32 uint32_t r; 33 size_t u, v, mlen; 34 35 buf = src; 36 37 /* 38 * First pass: determine whether the value fits. The 'r' value 39 * will contain the comparison result, as 0x00000000 (value is 40 * equal to the modulus), 0x00000001 (value is greater than the 41 * modulus), or 0xFFFFFFFF (value is lower than the modulus). 42 */ 43 mlen = (m[0] + 7) >> 3; 44 r = 0; 45 for (u = (mlen > len) ? mlen : len; u > 0; u --) { 46 uint32_t mb, xb; 47 48 v = u - 1; 49 if (v >= mlen) { 50 mb = 0; 51 } else { 52 mb = (m[1 + (v >> 2)] >> ((v & 3) << 3)) & 0xFF; 53 } 54 if (v >= len) { 55 xb = 0; 56 } else { 57 xb = buf[len - u]; 58 } 59 r = MUX(EQ(r, 0), (uint32_t)CMP(xb, mb), r); 60 } 61 62 /* 63 * Only r == 0xFFFFFFFF is acceptable. We want to set r to 0xFF if 64 * the value fits, 0x00 otherwise. 65 */ 66 r >>= 24; 67 br_i32_zero(x, m[0]); 68 u = (mlen > len) ? len : mlen; 69 while (u > 0) { 70 uint32_t xb; 71 72 xb = buf[len - u] & r; 73 u --; 74 x[1 + (u >> 2)] |= xb << ((u & 3) << 3); 75 } 76 return r >> 7; 77 } 78