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simplify delta compression algorithm

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This commit is contained in:
YamaArashi 2017-01-08 16:54:21 -08:00
parent e2daa41862
commit 42e277b298
1 changed files with 39 additions and 79 deletions
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118
tools/aif2pcm/main.c
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@ -23,6 +23,7 @@
#include <string.h>
#include <stdbool.h>
#include <stdint.h>
#include <limits.h>
/* extended.c */
void ieee754_write_extended (double, uint8_t*);
@ -287,7 +288,7 @@ void read_aif(struct Bytes *aif, AifData *aif_data)
}
// This is a table of deltas between sample values in compressed PCM data.
const int8_t gDeltaEncodingTable[] = {
const int gDeltaEncodingTable[] = {
0, 1, 4, 9, 16, 25, 36, 49,
-64, -49, -36, -25, -16, -9, -4, -1,
};
@ -359,6 +360,26 @@ struct Bytes *delta_decompress(struct Bytes *delta, unsigned int expected_length
return pcm;
}
int get_delta_index(uint8_t sample, uint8_t prev_sample)
{
int best_error = INT_MAX;
int best_index = -1;
for (int i = 0; i < 16; i++)
{
uint8_t new_sample = prev_sample + gDeltaEncodingTable[i];
int error = sample > new_sample ? sample - new_sample : new_sample - sample;
if (error < best_error)
{
best_error = error;
best_index = i;
}
}
return best_index;
}
struct Bytes *delta_compress(struct Bytes *pcm)
{
struct Bytes *delta = malloc(sizeof(struct Bytes));
@ -384,103 +405,42 @@ struct Bytes *delta_compress(struct Bytes *pcm)
delta->data = malloc(delta->length + 33);
uint8_t hi, lo;
unsigned int i = 0;
unsigned int j = 0;
int k;
int l;
int8_t base;
int8_t diff;
uint8_t base;
int delta_index;
while (i < pcm->length)
{
base = (int8_t)pcm->data[i++];
delta->data[j++] = (uint8_t)base;
if (i >= pcm->length)
{
break;
}
hi = 0;
diff = ((int8_t)pcm->data[i++]) - base;
if (diff > 49) diff = 49;
if (diff < -64) diff = -64;
if (diff < 0)
{
for (l = 8; l < 16; l++)
{
lo = l & 0xf;
if (diff <= gDeltaEncodingTable[l]) break;
}
}
else
{
for (l = 0; l < 8; l++)
{
lo = l & 0xf;
if (diff <= gDeltaEncodingTable[l]) break;
}
}
base += diff;
delta->data[j++] = (hi << 4) | lo;
base = pcm->data[i++];
delta->data[j++] = base;
if (i >= pcm->length)
{
break;
}
delta_index = get_delta_index(pcm->data[i++], base);
base += gDeltaEncodingTable[delta_index];
delta->data[j++] = delta_index;
for (k = 0; k < 31; k++)
{
diff = ((int8_t)pcm->data[i++]) - base;
if (diff > 49) diff = 49;
if (diff < -64) diff = -64;
if (diff < 0)
{
for (l = 8; l < 16; l++)
{
hi = l & 0xf;
if (diff <= gDeltaEncodingTable[l]) break;
}
}
else
{
for (l = 0; l < 8; l++)
{
hi = l & 0xf;
if (diff <= gDeltaEncodingTable[l]) break;
}
}
base += diff;
delta->data[j] = (hi << 4);
if (i >= pcm->length)
{
break;
}
diff = ((int8_t)pcm->data[i++]) - base;
if (diff > 49) diff = 49;
if (diff < -64) diff = -64;
if (diff < 0)
{
for (l = 8; l < 16; l++)
{
lo = l & 0xf;
if (diff <= gDeltaEncodingTable[l]) break;
}
}
else
{
for (l = 0; l < 8; l++)
{
lo = l & 0xf;
if (diff <= gDeltaEncodingTable[l]) break;
}
}
base += diff;
delta->data[j++] = (hi << 4) | lo;
delta_index = get_delta_index(pcm->data[i++], base);
base += gDeltaEncodingTable[delta_index];
delta->data[j] = (delta_index << 4);
if (i >= pcm->length)
{
break;
}
}
if (i >= pcm->length)
{
break;
delta_index = get_delta_index(pcm->data[i++], base);
base += gDeltaEncodingTable[delta_index];
delta->data[j++] |= delta_index;
}
}