/*
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* Copyright 2011 Google Inc.
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#include "SkPackBits.h"
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#include "SkTo.h"
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#include <cstring>
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size_t SkPackBits::ComputeMaxSize8(size_t srcSize) {
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// worst case is the number of 8bit values + 1 byte per (up to) 128 entries.
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return ((srcSize + 127) >> 7) + srcSize;
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}
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static uint8_t* flush_same8(uint8_t dst[], uint8_t value, size_t count) {
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while (count > 0) {
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size_t n = count > 128 ? 128 : count;
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*dst++ = (uint8_t)(n - 1);
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*dst++ = (uint8_t)value;
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count -= n;
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}
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return dst;
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}
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static uint8_t* flush_diff8(uint8_t* SK_RESTRICT dst,
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const uint8_t* SK_RESTRICT src, size_t count) {
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while (count > 0) {
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size_t n = count > 128 ? 128 : count;
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*dst++ = (uint8_t)(n + 127);
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memcpy(dst, src, n);
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src += n;
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dst += n;
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count -= n;
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}
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return dst;
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}
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size_t SkPackBits::Pack8(const uint8_t* SK_RESTRICT src, size_t srcSize,
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uint8_t* SK_RESTRICT dst, size_t dstSize) {
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if (dstSize < ComputeMaxSize8(srcSize)) {
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return 0;
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}
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uint8_t* const origDst = dst;
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const uint8_t* stop = src + srcSize;
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for (intptr_t count = stop - src; count > 0; count = stop - src) {
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if (1 == count) {
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*dst++ = 0;
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*dst++ = *src;
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break;
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}
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unsigned value = *src;
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const uint8_t* s = src + 1;
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if (*s == value) { // accumulate same values...
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do {
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s++;
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if (s == stop) {
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break;
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}
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} while (*s == value);
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dst = flush_same8(dst, value, SkToInt(s - src));
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} else { // accumulate diff values...
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do {
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if (++s == stop) {
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goto FLUSH_DIFF;
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}
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// only stop if we hit 3 in a row,
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// otherwise we get bigger than compuatemax
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} while (*s != s[-1] || s[-1] != s[-2]);
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s -= 2; // back up so we don't grab the "same" values that follow
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FLUSH_DIFF:
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dst = flush_diff8(dst, src, SkToInt(s - src));
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}
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src = s;
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}
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return dst - origDst;
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}
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int SkPackBits::Unpack8(const uint8_t* SK_RESTRICT src, size_t srcSize,
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uint8_t* SK_RESTRICT dst, size_t dstSize) {
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uint8_t* const origDst = dst;
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uint8_t* const endDst = dst + dstSize;
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const uint8_t* stop = src + srcSize;
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while (src < stop) {
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unsigned n = *src++;
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if (n <= 127) { // repeat count (n + 1)
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n += 1;
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if (dst > (endDst - n) || src >= stop) {
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return 0;
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}
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memset(dst, *src++, n);
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} else { // same count (n - 127)
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n -= 127;
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if (dst > (endDst - n) || src > (stop - n)) {
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return 0;
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}
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memcpy(dst, src, n);
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src += n;
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}
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dst += n;
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}
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SkASSERT(src <= stop);
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SkASSERT(dst <= endDst);
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return SkToInt(dst - origDst);
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}
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