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avcodec/exr: add lut oriented half to float conversion code

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This commit is contained in:
Paul B Mahol 2021-02-28 12:44:25 +01:00
parent cf2f8dcc6a
commit 6cc3ba4be6
2 changed files with 103 additions and 73 deletions
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102
libavcodec/exr.c
View File

@ -29,8 +29,6 @@
*
* For more information on the OpenEXR format, visit:
* http://openexr.com/
*
* exr_half2float() is credited to Aaftab Munshi, Dan Ginsburg, Dave Shreiner.
*/
#include <float.h>
@ -54,6 +52,7 @@
#include "exrdsp.h"
#include "get_bits.h"
#include "internal.h"
#include "half2float.h"
#include "mathops.h"
#include "thread.h"
@ -190,69 +189,12 @@ typedef struct EXRContext {
enum AVColorTransferCharacteristic apply_trc_type;
float gamma;
union av_intfloat32 gamma_table[65536];
uint32_t mantissatable[2048];
uint32_t exponenttable[64];
uint16_t offsettable[64];
} EXRContext;
/* -15 stored using a single precision bias of 127 */
#define HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP 0x38000000
/* max exponent value in single precision that will be converted
* to Inf or Nan when stored as a half-float */
#define HALF_FLOAT_MAX_BIASED_EXP_AS_SINGLE_FP_EXP 0x47800000
/* 255 is the max exponent biased value */
#define FLOAT_MAX_BIASED_EXP (0xFF << 23)
#define HALF_FLOAT_MAX_BIASED_EXP (0x1F << 10)
/**
* Convert a half float as a uint16_t into a full float.
*
* @param hf half float as uint16_t
*
* @return float value
*/
static union av_intfloat32 exr_half2float(uint16_t hf)
{
unsigned int sign = (unsigned int) (hf >> 15);
unsigned int mantissa = (unsigned int) (hf & ((1 << 10) - 1));
unsigned int exp = (unsigned int) (hf & HALF_FLOAT_MAX_BIASED_EXP);
union av_intfloat32 f;
if (exp == HALF_FLOAT_MAX_BIASED_EXP) {
// we have a half-float NaN or Inf
// half-float NaNs will be converted to a single precision NaN
// half-float Infs will be converted to a single precision Inf
exp = FLOAT_MAX_BIASED_EXP;
mantissa <<= 13; // preserve half-float NaN bits if set
} else if (exp == 0x0) {
// convert half-float zero/denorm to single precision value
if (mantissa) {
mantissa <<= 1;
exp = HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP;
// check for leading 1 in denorm mantissa
while (!(mantissa & (1 << 10))) {
// for every leading 0, decrement single precision exponent by 1
// and shift half-float mantissa value to the left
mantissa <<= 1;
exp -= (1 << 23);
}
// clamp the mantissa to 10 bits
mantissa &= ((1 << 10) - 1);
// shift left to generate single-precision mantissa of 23 bits
mantissa <<= 13;
}
} else {
// shift left to generate single-precision mantissa of 23 bits
mantissa <<= 13;
// generate single precision biased exponent value
exp = (exp << 13) + HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP;
}
f.i = (sign << 31) | exp | mantissa;
return f;
}
static int zip_uncompress(EXRContext *s, const uint8_t *src, int compressed_size,
int uncompressed_size, EXRThreadData *td)
{
@ -951,7 +893,10 @@ static int ac_uncompress(EXRContext *s, GetByteContext *gb, float *block)
n += val & 0xff;
} else {
ret = n;
block[ff_zigzag_direct[n]] = exr_half2float(val).f;
block[ff_zigzag_direct[n]] = av_int2float(half2float(val,
s->mantissatable,
s->exponenttable,
s->offsettable));
n++;
}
}
@ -1161,10 +1106,12 @@ static int dwa_uncompress(EXRContext *s, const uint8_t *src, int compressed_size
float *block = td->block[j];
const int idx = (x >> 3) + (y >> 3) * dc_w + dc_w * dc_h * j;
uint16_t *dc = (uint16_t *)td->dc_data;
float dc_val = dc[idx];
union av_intfloat32 dc_val;
dc_val = exr_half2float(dc_val).f;
block[0] = dc_val;
dc_val.i = half2float(dc[idx], s->mantissatable,
s->exponenttable, s->offsettable);
block[0] = dc_val.f;
ac_uncompress(s, &agb, block);
dct_inverse(block);
}
@ -1209,8 +1156,11 @@ static int dwa_uncompress(EXRContext *s, const uint8_t *src, int compressed_size
uint8_t *ai0 = td->rle_raw_data + y * td->xsize;
uint8_t *ai1 = td->rle_raw_data + y * td->xsize + rle_raw_size / 2;
for (int x = 0; x < td->xsize; x++)
ao[x] = exr_half2float(ai0[x] | (ai1[x] << 8)).i;
for (int x = 0; x < td->xsize; x++) {
uint16_t ha = ai0[x] | (ai1[x] << 8);
ao[x] = half2float(ha, s->mantissatable, s->exponenttable, s->offsettable);
}
}
return 0;
@ -1455,7 +1405,11 @@ static int decode_block(AVCodecContext *avctx, void *tdata,
}
} else {
for (x = 0; x < xsize; x++) {
*ptr_x++ = exr_half2float(bytestream_get_le16(&src));
ptr_x[0].i = half2float(bytestream_get_le16(&src),
s->mantissatable,
s->exponenttable,
s->offsettable);
ptr_x++;
}
}
}
@ -2242,6 +2196,8 @@ static av_cold int decode_init(AVCodecContext *avctx)
float one_gamma = 1.0f / s->gamma;
avpriv_trc_function trc_func = NULL;
half2float_table(s->mantissatable, s->exponenttable, s->offsettable);
s->avctx = avctx;
ff_exrdsp_init(&s->dsp);
@ -2253,18 +2209,18 @@ static av_cold int decode_init(AVCodecContext *avctx)
trc_func = avpriv_get_trc_function_from_trc(s->apply_trc_type);
if (trc_func) {
for (i = 0; i < 65536; ++i) {
t = exr_half2float(i);
t.i = half2float(i, s->mantissatable, s->exponenttable, s->offsettable);
t.f = trc_func(t.f);
s->gamma_table[i] = t;
}
} else {
if (one_gamma > 0.9999f && one_gamma < 1.0001f) {
for (i = 0; i < 65536; ++i) {
s->gamma_table[i] = exr_half2float(i);
s->gamma_table[i].i = half2float(i, s->mantissatable, s->exponenttable, s->offsettable);
}
} else {
for (i = 0; i < 65536; ++i) {
t = exr_half2float(i);
t.i = half2float(i, s->mantissatable, s->exponenttable, s->offsettable);
/* If negative value we reuse half value */
if (t.f <= 0.0f) {
s->gamma_table[i] = t;

74
libavcodec/half2float.h Normal file
View File

@ -0,0 +1,74 @@
/*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef AVCODEC_HALF2FLOAT_H
#define AVCODEC_HALF2FLOAT_H
#include <stdint.h>
static uint32_t convertmantissa(uint32_t i)
{
uint32_t m = i << 13; // Zero pad mantissa bits
uint32_t e = 0; // Zero exponent
while (!(m & 0x00800000UL)){ // While not normalized
e -= 0x00800000UL; // Decrement exponent (1<<23)
m <<= 1; // Shift mantissa
}
m &= ~0x00800000UL; // Clear leading 1 bit
e += 0x38800000UL; // Adjust bias ((127-14)<<23)
return m | e; // Return combined number
}
static void half2float_table(uint32_t *mantissatable, uint32_t *exponenttable,
uint16_t *offsettable)
{
mantissatable[0] = 0;
for (int i = 1; i < 1024; i++)
mantissatable[i] = convertmantissa(i);
for (int i = 1024; i < 2048; i++)
mantissatable[i] = 0x38000000UL + ((i - 1024) << 13UL);
exponenttable[0] = 0;
for (int i = 1; i < 31; i++)
exponenttable[i] = i << 23;
for (int i = 33; i < 63; i++)
exponenttable[i] = 0x80000000UL + ((i - 32) << 23UL);
exponenttable[31]= 0x47800000UL;
exponenttable[32]= 0x80000000UL;
exponenttable[63]= 0xC7800000UL;
offsettable[0] = 0;
for (int i = 1; i < 64; i++)
offsettable[i] = 1024;
offsettable[32] = 0;
}
static uint32_t half2float(uint16_t h, uint32_t *mantissatable, uint32_t *exponenttable,
uint16_t *offsettable)
{
uint32_t f;
f = mantissatable[offsettable[h >> 10] + (h & 0x3ff)] + exponenttable[h >> 10];
return f;
}
#endif /* AVCODEC_HALF2FLOAT_H */