1 /* Copyright (c) 2001-2011 Timothy B. Terriberry 2 */ 3 /* 4 Redistribution and use in source and binary forms, with or without 5 modification, are permitted provided that the following conditions 6 are met: 7 8 - Redistributions of source code must retain the above copyright 9 notice, this list of conditions and the following disclaimer. 10 11 - Redistributions in binary form must reproduce the above copyright 12 notice, this list of conditions and the following disclaimer in the 13 documentation and/or other materials provided with the distribution. 14 15 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 16 ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 17 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 18 A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER 19 OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 20 EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 21 PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 22 PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 23 LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 24 NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 25 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28 #ifdef HAVE_CONFIG_H 29 #include "config.h" 30 #endif 31 32 #include "entcode.h" 33 #include "arch.h" 34 35 #if !defined(EC_CLZ) 36 /*This is a fallback for systems where we don't know how to access 37 a BSR or CLZ instruction (see ecintrin.h). 38 If you are optimizing Opus on a new platform and it has a native CLZ or 39 BZR (e.g. cell, MIPS, x86, etc) then making it available to Opus will be 40 an easy performance win.*/ 41 int ec_ilog(opus_uint32 _v){ 42 /*On a Pentium M, this branchless version tested as the fastest on 43 1,000,000,000 random 32-bit integers, edging out a similar version with 44 branches, and a 256-entry LUT version.*/ 45 int ret; 46 int m; 47 ret=!!_v; 48 m=!!(_v&0xFFFF0000)<<4; 49 _v>>=m; 50 ret|=m; 51 m=!!(_v&0xFF00)<<3; 52 _v>>=m; 53 ret|=m; 54 m=!!(_v&0xF0)<<2; 55 _v>>=m; 56 ret|=m; 57 m=!!(_v&0xC)<<1; 58 _v>>=m; 59 ret|=m; 60 ret+=!!(_v&0x2); 61 return ret; 62 } 63 #endif 64 65 opus_uint32 ec_tell_frac(ec_ctx *_this){ 66 opus_uint32 nbits; 67 opus_uint32 r; 68 int l; 69 int i; 70 /*To handle the non-integral number of bits still left in the encoder/decoder 71 state, we compute the worst-case number of bits of val that must be 72 encoded to ensure that the value is inside the range for any possible 73 subsequent bits. 74 The computation here is independent of val itself (the decoder does not 75 even track that value), even though the real number of bits used after 76 ec_enc_done() may be 1 smaller if rng is a power of two and the 77 corresponding trailing bits of val are all zeros. 78 If we did try to track that special case, then coding a value with a 79 probability of 1/(1<<n) might sometimes appear to use more than n bits. 80 This may help explain the surprising result that a newly initialized 81 encoder or decoder claims to have used 1 bit.*/ 82 nbits=_this->nbits_total<<BITRES; 83 l=EC_ILOG(_this->rng); 84 r=_this->rng>>(l-16); 85 for(i=BITRES;i-->0;){ 86 int b; 87 r=r*r>>15; 88 b=(int)(r>>16); 89 l=l<<1|b; 90 r>>=b; 91 } 92 return nbits-l; 93 } 94
