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Add bitstream constr

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This commit is contained in:
atxr 2024-02-20 12:29:33 +01:00
parent 3449b9edbf
commit 92d805659b
2 changed files with 27 additions and 14 deletions
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5
libmineziper/include/libmineziper_bitstream.h
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@ -3,7 +3,7 @@
typedef struct bitstream typedef struct bitstream
{ {
char *data; unsigned char *data;
int data_size; // size of 'data' array int data_size; // size of 'data' array
int last_bit_offset; // last bit in the stream int last_bit_offset; // last bit in the stream
@ -13,8 +13,9 @@ typedef struct bitstream
int current_bit_offset; // which bit we are currently reading/writing int current_bit_offset; // which bit we are currently reading/writing
} bitstream; } bitstream;
char get_bits(bitstream *bs, unsigned int size); unsigned int get_bits(bitstream *bs, unsigned int size);
void print_bits(int x, int size); void print_bits(int x, int size);
unsigned int reverse(unsigned int x, unsigned int numBits); unsigned int reverse(unsigned int x, unsigned int numBits);
bitstream init_bitstream(char *data, int size, int last_bit_offset);
#endif #endif

36
libmineziper/src/libmineziper_bitstream.c
View file

@ -2,23 +2,22 @@
#include <assert.h> #include <assert.h>
char get_bits(bitstream *bs, unsigned int size) unsigned int get_bits(bitstream* bs, unsigned int bit_num)
{ {
if (size > 32) if (bit_num > 32)
return -1; return -1;
if (size == 0) if (bit_num == 0)
return 0; return 0;
int out; int out;
if (bs->current_bit_offset + size <= 8) if (bs->current_bit_offset + bit_num <= 8)
{ {
int mask = (1 << size) - 1; int mask = (1 << bit_num) - 1;
mask <<= bs->current_bit_offset;
out = bs->data[bs->current_data_offset] & mask; out = (bs->data[bs->current_data_offset] >> bs->current_bit_offset) & mask;
bs->current_bit_offset += size; bs->current_bit_offset += bit_num;
if (bs->current_bit_offset == 8) if (bs->current_bit_offset == 8)
{ {
bs->current_bit_offset = 0; bs->current_bit_offset = 0;
@ -28,8 +27,9 @@ char get_bits(bitstream *bs, unsigned int size)
else else
{ {
int diff = 8 - bs->current_bit_offset; int diff = 8 - bs->current_bit_offset;
int next = (bs->current_bit_offset + bit_num) % 8;
out = get_bits(bs, diff); out = get_bits(bs, diff);
out += get_bits(bs, (bs->current_bit_offset + size) % 8); out += get_bits(bs, next) << diff;
} }
return out; return out;
@ -92,11 +92,23 @@ int get_bit_length(int x)
return n; return n;
} }
void print_bits(int x, int size) void print_bits(int x, int bit_num)
{ {
for (int i = size - 1; i >= 0; i--) for (int i = bit_num - 1; i >= 0; i--)
{ {
printf("%c", 0b1 & (x >> i) ? '1' : '0'); printf("%c", 0b1 & (x >> i) ? '1' : '0');
} }
printf("(%d,%d)", x, size); printf("(%d,%d)", x, bit_num);
}
bitstream init_bitstream(char* data, int size, int last_bit_offset)
{
bitstream bs = {
.current_bit_offset = 0,
.current_data_offset = 0,
.data = data,
.data_size = size,
.last_bit_offset = last_bit_offset};
return bs;
} }