ref: 6622002197992ffd2789e07e39e1f9df8cbf0d0c
dir: /src/getbits.c/
/* * Copyright © 2018, VideoLAN and dav1d authors * Copyright © 2018, Two Orioles, LLC * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are met: * * 1. Redistributions of source code must retain the above copyright notice, this * list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright notice, * this list of conditions and the following disclaimer in the documentation * and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ #include "config.h" #include <assert.h> #include "common/intops.h" #include "src/getbits.h" void init_get_bits(GetBits *const c, const uint8_t *const data, const size_t sz) { c->ptr = c->ptr_start = data; c->ptr_end = &c->ptr_start[sz]; c->bits_left = 0; c->state = 0; c->error = 0; c->eof = 0; } static void refill(GetBits *const c, const unsigned n) { assert(c->bits_left <= 56); uint64_t state = 0; do { state <<= 8; c->bits_left += 8; if (!c->eof) state |= *c->ptr++; if (c->ptr >= c->ptr_end) { c->error = c->eof; c->eof = 1; } } while (n > c->bits_left); c->state |= state << (64 - c->bits_left); } unsigned get_bits(GetBits *const c, const unsigned n) { assert(n <= 32 /* can go up to 57 if we change return type */); if (n > c->bits_left) refill(c, n); const uint64_t state = c->state; c->bits_left -= n; c->state <<= n; return state >> (64 - n); } int get_sbits(GetBits *const c, const unsigned n) { const int shift = 31 - n; const int res = get_bits(c, n + 1) << shift; return res >> shift; } unsigned get_uniform(GetBits *const c, const unsigned n) { assert(n > 0); const int l = ulog2(n) + 1; assert(l > 0); const int m = (1 << l) - n; const int v = get_bits(c, l - 1); return v < m ? v : (v << 1) - m + get_bits(c, 1); } unsigned get_vlc(GetBits *const c) { int n_bits = 0; while (!get_bits(c, 1)) n_bits++; if (n_bits >= 32) return 0xFFFFFFFFU; return ((1 << n_bits) - 1) + get_bits(c, n_bits); } static unsigned get_bits_subexp_u(GetBits *const c, const unsigned ref, const unsigned n) { unsigned v = 0; for (int i = 0;; i++) { const int b = i ? 3 + i - 1 : 3; if (n < v + 3 * (1 << b)) { v += get_uniform(c, n - v + 1); break; } if (!get_bits(c, 1)) { v += get_bits(c, b); break; } v += 1 << b; } return ref * 2 <= n ? inv_recenter(ref, v) : n - inv_recenter(n - ref, v); } int get_bits_subexp(GetBits *const c, const int ref, const unsigned n) { return (int) get_bits_subexp_u(c, ref + (1 << n), 2 << n) - (1 << n); } const uint8_t *flush_get_bits(GetBits *c) { c->bits_left = 0; c->state = 0; return c->ptr; }