int rv_decode_dc(MpegEncContext *s, int n)
{
int code;
if (n < 4) {
code = get_vlc(&s->gb, &rv_dc_lum);
if (code < 0) {
/* XXX: I don't understand why they use LONGER codes than
necessary. The following code would be completely useless
if they had thought about it !!! */
code = get_bits(&s->gb, 7);
if (code == 0x7c) {
code = (INT8)(get_bits(&s->gb, 7) + 1);
} else if (code == 0x7d) {
code = -128 + get_bits(&s->gb, 7);
} else if (code == 0x7e) {
if (get_bits(&s->gb, 1) == 0)
code = (INT8)(get_bits(&s->gb, 8) + 1);
else
code = (INT8)(get_bits(&s->gb, 8));
} else if (code == 0x7f) {
get_bits(&s->gb, 11);
code = 1;
}
} else {
code -= 128;
}
} else {
code = get_vlc(&s->gb, &rv_dc_chrom);
/* same remark */
if (code < 0) {
code = get_bits(&s->gb, 9);
if (code == 0x1fc) {
code = (INT8)(get_bits(&s->gb, 7) + 1);
} else if (code == 0x1fd) {
code = -128 + get_bits(&s->gb, 7);
} else if (code == 0x1fe) {
get_bits(&s->gb, 9);
code = 1;
} else {
return 0xffff;
}
} else {
code -= 128;
}
}
return -code;
}
int decode_ac(jpeg_ctx_t *ctx, int yuv_index, short mb[])
{
int code, len, val;
GetBitContext *gb = &ctx->getbit_ctx;
int ac_index = yuv_index ? 1 : 0;
int16_t (*table)[2] = ctx->dec_vlcs[1][ac_index].table;
int zero_num = 0;
while (zero_num < 63)
{
code = get_vlc(gb, table);
if (code < 0)
{
log("JO: format wrong, huffman decode fail in decode_ac\n");
return -1;
}
zero_num += code >> 4; //尼玛, 构造vlc时篡改符号值，每个符号加了16，原来就是了这里能够自动zero_num + 1啊，太扣效率了吧
len = code & 0xf;
if (len)
{
val = get_xbits(gb, len);
mb[zero_num] = (short)val;
}
}
return 0;
}
int decode_dc(jpeg_ctx_t *ctx, int yuv_index, short mb[])
{
int code, val;
code = get_vlc(&ctx->getbit_ctx, ctx->dec_vlcs[0][yuv_index ? 1 : 0].table);
if (code < 0)
{
log("JO: format wrong, huffman decode fail in decode_dc\n");
return -1;
}
if (code)
{
val = get_xbits(&ctx->getbit_ctx, code);
mb[0] = (short)val;
}
return 0;
}
