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Wrote bitwise reader; needs tests

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This commit is contained in:
Dan Hirsch 2012-04-23 19:39:44 +01:00
parent 5ee7865458
commit 7adae0da7c
4 changed files with 67 additions and 5 deletions
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49
src/bitreader.c Normal file
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#include <stdint.h>
#include "internal.h"
#include "hammer.h"
#define LSB(range) (0:range)
#define MSB(range) (1:range)
#define LDB(range,i) (((i)>>LSB(range))&((1<<(MSB(range)-LSB(range)+1))-1))
long long read_bits(parse_state_t* state, int count) {
long long out = 0;
int offset = 0;
while (count) {
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);
state->index++;
state->bit_offset = 0;
} else {
segment_len = count;
segment = (state->input[state->index] >> state->bit_offset) & ((1 << segment_len) - 1);
state->bit_offset += segment_len;
}
}
// have a valid segment; time to assemble the byte
if (state->endianness & BYTE_BIG_ENDIAN) {
out = out << segment_len | segment;
} else { // BYTE_LITTLE_ENDIAN
out |= segment << offset;
offset += segment_len;
}
count -= segment_len;
}
return out;
}