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 void 29 br_i31_mulacc(uint32_t *d, const uint32_t *a, const uint32_t *b) 30 { 31 size_t alen, blen, u; 32 uint32_t dl, dh; 33 34 alen = (a[0] + 31) >> 5; 35 blen = (b[0] + 31) >> 5; 36 37 /* 38 * We want to add the two bit lengths, but these are encoded, 39 * which requires some extra care. 40 */ 41 dl = (a[0] & 31) + (b[0] & 31); 42 dh = (a[0] >> 5) + (b[0] >> 5); 43 d[0] = (dh << 5) + dl + (~(uint32_t)(dl - 31) >> 31); 44 45 for (u = 0; u < blen; u ++) { 46 uint32_t f; 47 size_t v; 48 49 /* 50 * Carry always fits on 31 bits; we want to keep it in a 51 * 32-bit register on 32-bit architectures (on a 64-bit 52 * architecture, cast down from 64 to 32 bits means 53 * clearing the high bits, which is not free; on a 32-bit 54 * architecture, the same operation really means ignoring 55 * the top register, which has negative or zero cost). 56 */ 57 #if BR_64 58 uint64_t cc; 59 #else 60 uint32_t cc; 61 #endif 62 63 f = b[1 + u]; 64 cc = 0; 65 for (v = 0; v < alen; v ++) { 66 uint64_t z; 67 68 z = (uint64_t)d[1 + u + v] + MUL31(f, a[1 + v]) + cc; 69 cc = z >> 31; 70 d[1 + u + v] = (uint32_t)z & 0x7FFFFFFF; 71 } 72 d[1 + u + alen] = (uint32_t)cc; 73 } 74 } 75