On Thu, Aug 23, 2018 at 08:13:13PM +0200, Martin Vignali wrote:
[...]
> swscale_internal.h | 2 -
> utils.c | 70
> ++++++++++++++++++++++++++++++++++++++++++++++++++---
> 2 files changed, 68 insertions(+), 4 deletions(-)
> 911c6d681b09ab719e2c8abe337887732c28b65e
> 0003-swscale-add-bit_exact-lut-creation-for-8bit-to-float.patch
> From e7b78d6416189a72695dac0680782a987c84b274 Mon Sep 17 00:00:00 2001
> From: Martin Vignali <martin.vign...@gmail.com>
> Date: Thu, 23 Aug 2018 18:40:54 +0200
> Subject: [PATCH 3/4] swscale : add bit_exact lut creation for 8bit to float
>
> ---
> libswscale/swscale_internal.h | 2 +-
> libswscale/utils.c | 70
> +++++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 68 insertions(+), 4 deletions(-)
>
> diff --git a/libswscale/swscale_internal.h b/libswscale/swscale_internal.h
> index 3b6b682d5f..a9cd7bc8d7 100644
> --- a/libswscale/swscale_internal.h
> +++ b/libswscale/swscale_internal.h
> @@ -336,7 +336,7 @@ typedef struct SwsContext {
> uint32_t pal_yuv[256];
> uint32_t pal_rgb[256];
>
> - float uint2float_lut[256];
> + float *uint2float_lut; /*! store uint8 to float or uint16 to float */
>
> /**
> * @name Scaled horizontal lines ring buffer.
> diff --git a/libswscale/utils.c b/libswscale/utils.c
> index 5e56371180..ce65467c35 100644
> --- a/libswscale/utils.c
> +++ b/libswscale/utils.c
> @@ -1098,6 +1098,69 @@ static uint16_t * alloc_gamma_tbl(double e)
> return tbl;
> }
>
> +static void inline fill_uint_to_float_lut(SwsContext *c, int bitdepth) {
> + static const float float_mult8 = 1.0f / 255.0f;
> + int i;
> +
> + if (bitdepth == 8) { /*! fill uint8 to float lut */
> + for (i = 0; i < 256; ++i){
> + c->uint2float_lut[i] = (float)i * float_mult8;
> + }
> + } else { /*! unsupported bitdepth */
> + av_assert0(0);
> + }
> +}
> +
> +#define SIGN_EXP_MANT_TO_UINT32(sign, exp, mant) sign << 31 | exp << 23 |
> mant
> +
> +static void inline fill_uint_to_float_lut_bitexact(SwsContext *c, int
> bitdepth) {
> + int i, j, exp, mant, div;
> + uint32_t off_coeff_mant;
> + uint32_t coeff_mant;
> + uint32_t *lut = (uint32_t *)c->uint2float_lut;
> + int min_loop = 1;
> + int max_loop = 2;
> +
> + if (bitdepth == 8) { /*! fill uint8 to float lut */
> + lut[0] = 0;
> + lut[1] = SIGN_EXP_MANT_TO_UINT32(0, 119, 32897);
> +
> + exp = 119; /*! initial exp */
> + off_coeff_mant = coeff_mant = 4210752;
> +
> + for (j = 0; j < 7; ++j) {
> + exp++;
> + min_loop *= 2;
> + max_loop *= 2;
> + div = (max_loop - 1 - min_loop);
> +
> + for (i = min_loop; i < max_loop; ++i) {
> + mant = (i - min_loop) * coeff_mant / div + 32897;
> + lut[i] = SIGN_EXP_MANT_TO_UINT32(0, exp, mant);
> + }
> +
> + if (j < 6) {
> + off_coeff_mant >>= 1;
> + coeff_mant |= off_coeff_mant;
> + }
> + }
> + lut[255] = SIGN_EXP_MANT_TO_UINT32(0, 127, 0);
> + } else { /*! unsupported bitdepth */
> + av_assert0(0);
> + }
> +}
> +
> +static void alloc_uint_to_float_lut(SwsContext *c, int bitdepth) {
> + c->uint2float_lut = (float*)av_malloc(sizeof(float) * 1 << bitdepth);
> + if (!c->uint2float_lut)
> + return;
> + if (c->flags & SWS_BITEXACT) {
> + fill_uint_to_float_lut_bitexact(c, bitdepth);
> + } else {
> + fill_uint_to_float_lut(c, bitdepth);
> + }
is this complexity really needed ?
does the LUT generation code produce different results on platforms ?
if so i would suggest to try to use double and to add a small offset if needed
a 8bit table has 256 entries, a 16bit table 65536
a difference would occur if a source value from 64bit floats gets rounded
differently to 32bit floats. If this occurs a small offset could be added
so that none of the 65536 cases end up close to being between 2 32bit floats
This would avoid teh rather complex code if it works
thx
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
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