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Fix #118

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NEWS:
* Switching endianness mid-byte no longer potentially re-reads bytes.
* bit_offset now consistently refers to the number of bits already
  read.
* HParsedTokens now have a bit_length field; this is a size_t.  This
  may be removed for memory reasons.

The bit writer has not yet been updated to match; the result of
switching bit writer endianness in the middle of a byte remains
undefined.
This commit is contained in:
TQ Hirsch 2015-01-04 04:00:09 +01:00
parent 58af99ae40
commit af73181cf4
12 changed files with 86 additions and 48 deletions
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37
src/bitreader.c
View file

@ -39,10 +39,7 @@ int64_t h_read_bits(HInputStream* state, int count, char signed_p) {
if (bits_left <= 64) { // Large enough to handle any valid count, but small enough that overflow isn't a problem.
// not in danger of overflowing, so add in bits
// add in number of bits...
if (state->endianness & BIT_BIG_ENDIAN)
bits_left = (bits_left << 3) - 8 + state->bit_offset;
else
bits_left = (bits_left << 3) - state->bit_offset;
bits_left = (bits_left << 3) - state->bit_offset - state->margin;
if (bits_left < count) {
if (state->endianness & BYTE_BIG_ENDIAN)
final_shift = count - bits_left;
@ -54,7 +51,7 @@ int64_t h_read_bits(HInputStream* state, int count, char signed_p) {
final_shift = 0;
}
if ((state->bit_offset & 0x7) == 0 && (count & 0x7) == 0) {
if ((state->bit_offset & 0x7) == 0 && (count & 0x7) == 0 && (state->margin == 0)) {
// fast path
if (state->endianness & BYTE_BIG_ENDIAN) {
while (count > 0) {
@ -73,22 +70,24 @@ int64_t h_read_bits(HInputStream* state, int count, char signed_p) {
int segment, segment_len;
// Read a segment...
if (state->endianness & BIT_BIG_ENDIAN) {
if (count >= state->bit_offset) {
segment_len = state->bit_offset;
state->bit_offset = 8;
segment = state->input[state->index] & ((1 << segment_len) - 1);
state->index++;
} else {
segment_len = count;
state->bit_offset -= count;
segment = (state->input[state->index] >> state->bit_offset) & ((1 << segment_len) - 1);
}
} else { // BIT_LITTLE_ENDIAN
if (count + state->bit_offset >= 8) {
segment_len = 8 - state->bit_offset;
segment = (state->input[state->index] >> state->bit_offset);
if (count + state->bit_offset + state->margin >= 8) {
segment_len = 8 - state->bit_offset - state->margin;
segment = (state->input[state->index] >> state->margin) & ((1 << segment_len) - 1);
state->index++;
state->bit_offset = 0;
state->margin = 0;
} else {
segment_len = count;
state->bit_offset += count;
segment = (state->input[state->index] >> (8 - state->bit_offset)) & ((1 << segment_len) - 1);
}
} else { // BIT_LITTLE_ENDIAN
if (count + state->bit_offset + state->margin >= 8) {
segment_len = 8 - state->bit_offset - state->margin;
segment = (state->input[state->index] >> state->bit_offset) & ((1 << segment_len) - 1);
state->index++;
state->bit_offset = 0;
state->margin = 0;
} else {
segment_len = count;
segment = (state->input[state->index] >> state->bit_offset) & ((1 << segment_len) - 1);