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avcodec/hqx: Simplify deriving AC table index

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It can be simply encoded in the quant coefficients itself
as they are so small.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt
2025-03-13 22:52:15 +01:00
parent 2f4f96f1ac
commit 8a2e84dc96
1 changed files with 30 additions and 31 deletions
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61
libavcodec/hqx.c
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@ -75,21 +75,27 @@ typedef struct HQXContext {
#define HQX_HEADER_SIZE 59
#define AC_IDX(q) ((q) >= 128 ? HQX_AC_Q128 : (q) >= 64 ? HQX_AC_Q64 : \
(q) >= 32 ? HQX_AC_Q32 : (q) >= 16 ? HQX_AC_Q16 : \
(q) >= 8 ? HQX_AC_Q8 : HQX_AC_Q0)
/* macroblock selects a group of 4 possible quants and
* a block can use any of those four quantisers
* one column is powers of 2, the other one is powers of 2 * 3,
* then there is the special one, powers of 2 * 5 */
static const int hqx_quants[16][4] = {
{ 0x1, 0x2, 0x4, 0x8 }, { 0x1, 0x3, 0x6, 0xC },
{ 0x2, 0x4, 0x8, 0x10 }, { 0x3, 0x6, 0xC, 0x18 },
{ 0x4, 0x8, 0x10, 0x20 }, { 0x6, 0xC, 0x18, 0x30 },
{ 0x8, 0x10, 0x20, 0x40 },
{ 0xA, 0x14, 0x28, 0x50 },
{ 0xC, 0x18, 0x30, 0x60 },
{ 0x10, 0x20, 0x40, 0x80 }, { 0x18, 0x30, 0x60, 0xC0 },
{ 0x20, 0x40, 0x80, 0x100 }, { 0x30, 0x60, 0xC0, 0x180 },
{ 0x40, 0x80, 0x100, 0x200 }, { 0x60, 0xC0, 0x180, 0x300 },
{ 0x80, 0x100, 0x200, 0x400 }
* then there is the special one, powers of 2 * 5.
* We also encode the corresponding AC index in these tables in bits 29-31. */
static const unsigned hqx_quants[16][4] = {
#define Q(q) ((unsigned)AC_IDX(q) << 29 | (q))
{ Q( 0x1), Q( 0x2), Q( 0x4), Q( 0x8) }, { Q( 0x1), Q( 0x3), Q( 0x6), Q( 0xC) },
{ Q( 0x2), Q( 0x4), Q( 0x8), Q( 0x10) }, { Q( 0x3), Q( 0x6), Q( 0xC), Q( 0x18) },
{ Q( 0x4), Q( 0x8), Q( 0x10), Q( 0x20) }, { Q( 0x6), Q( 0xC), Q( 0x18), Q( 0x30) },
{ Q( 0x8), Q( 0x10), Q( 0x20), Q( 0x40) },
{ Q(0xA), Q(0x14), Q(0x28), Q(0x50) },
{ Q( 0xC), Q(0x18), Q( 0x30), Q( 0x60) },
{ Q(0x10), Q( 0x20), Q( 0x40), Q( 0x80) }, { Q(0x18), Q(0x30), Q( 0x60), Q( 0xC0) },
{ Q(0x20), Q( 0x40), Q( 0x80), Q(0x100) }, { Q(0x30), Q(0x60), Q( 0xC0), Q(0x180) },
{ Q(0x40), Q( 0x80), Q(0x100), Q(0x200) }, { Q(0x60), Q(0xC0), Q(0x180), Q(0x300) },
{ Q(0x80), Q(0x100), Q(0x200), Q(0x400) }
};
static const uint8_t hqx_quant_luma[64] = {
@ -143,12 +149,12 @@ static inline void hqx_get_ac(GetBitContext *gb, const HQXAC *ac,
}
static int decode_block(GetBitContext *gb, const VLCElem vlc[],
const int *quants, int dcb,
const unsigned *quants, int dcb,
int16_t block[64], int *last_dc)
{
int q, dc;
int ac_idx;
int run, lev, pos = 0;
unsigned ac_idx, q;
int dc;
dc = get_vlc2(gb, vlc, HQX_DC_VLC_BITS, 2);
*last_dc += dc;
@ -156,18 +162,9 @@ static int decode_block(GetBitContext *gb, const VLCElem vlc[],
block[0] = sign_extend(*last_dc << (12 - dcb), 12);
q = quants[get_bits(gb, 2)];
if (q >= 128)
ac_idx = HQX_AC_Q128;
else if (q >= 64)
ac_idx = HQX_AC_Q64;
else if (q >= 32)
ac_idx = HQX_AC_Q32;
else if (q >= 16)
ac_idx = HQX_AC_Q16;
else if (q >= 8)
ac_idx = HQX_AC_Q8;
else
ac_idx = HQX_AC_Q0;
// ac_idx is encoded in the high bits of quants;
// because block is 16 bit, we do not even need to clear said bits.
ac_idx = q >> 29;
do {
hqx_get_ac(gb, &hqx_ac[ac_idx], &run, &lev);
@ -184,7 +181,7 @@ static int hqx_decode_422(HQXContext *ctx, int slice_no, int x, int y)
{
HQXSlice *slice = &ctx->slice[slice_no];
GetBitContext *gb = &slice->gb;
const int *quants;
const unsigned *quants;
int flag;
int last_dc;
int i, ret;
@ -219,7 +216,6 @@ static int hqx_decode_422a(HQXContext *ctx, int slice_no, int x, int y)
{
HQXSlice *slice = &ctx->slice[slice_no];
GetBitContext *gb = &slice->gb;
const int *quants;
int flag = 0;
int last_dc;
int i, ret;
@ -231,6 +227,8 @@ static int hqx_decode_422a(HQXContext *ctx, int slice_no, int x, int y)
cbp = get_vlc2(gb, cbp_vlc, HQX_CBP_VLC_BITS, 1);
if (cbp) {
const unsigned *quants;
if (ctx->interlaced)
flag = get_bits1(gb);
@ -267,7 +265,7 @@ static int hqx_decode_444(HQXContext *ctx, int slice_no, int x, int y)
{
HQXSlice *slice = &ctx->slice[slice_no];
GetBitContext *gb = &slice->gb;
const int *quants;
const unsigned *quants;
int flag;
int last_dc;
int i, ret;
@ -304,7 +302,6 @@ static int hqx_decode_444a(HQXContext *ctx, int slice_no, int x, int y)
{
HQXSlice *slice = &ctx->slice[slice_no];
GetBitContext *gb = &slice->gb;
const int *quants;
int flag = 0;
int last_dc;
int i, ret;
@ -316,6 +313,8 @@ static int hqx_decode_444a(HQXContext *ctx, int slice_no, int x, int y)
cbp = get_vlc2(gb, cbp_vlc, HQX_CBP_VLC_BITS, 1);
if (cbp) {
const unsigned *quants;
if (ctx->interlaced)
flag = get_bits1(gb);