Alexandre Lision | 744f742 | 2013-09-25 11:39:37 -0400 | [diff] [blame] | 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 | } |