[FFmpeg-devel] [PATCH 2/2] lavc/dxvenc: migrate DXT1 encoder to lavu hashtable
Andreas Rheinhardt
andreas.rheinhardt at outlook.com
Mon Feb 5 14:04:54 EET 2024
Connor Worley:
> Offers a modest performance gain due to the switch from naive linear
> probling to robin hood.
How much would one gain if the hash function knew that key_size and
val_size are four?
>
> Signed-off-by: Connor Worley <connorbworley at gmail.com>
> ---
> libavcodec/dxvenc.c | 121 +++++++++++++-------------------------------
> 1 file changed, 35 insertions(+), 86 deletions(-)
>
> diff --git a/libavcodec/dxvenc.c b/libavcodec/dxvenc.c
> index b274175689..e17b3b2c36 100644
> --- a/libavcodec/dxvenc.c
> +++ b/libavcodec/dxvenc.c
> @@ -21,7 +21,7 @@
>
> #include <stdint.h>
>
> -#include "libavutil/crc.h"
> +#include "libavutil/hashtable.h"
> #include "libavutil/imgutils.h"
> #include "libavutil/opt.h"
>
> @@ -44,69 +44,6 @@ enum DXVTextureFormat {
> DXV_FMT_DXT1 = MKBETAG('D', 'X', 'T', '1'),
> };
>
> -typedef struct HTEntry {
> - uint32_t key;
> - uint32_t pos;
> -} HTEntry;
> -
> -static void ht_init(HTEntry *ht)
> -{
> - for (size_t i = 0; i < LOOKBACK_HT_ELEMS; i++) {
> - ht[i].pos = -1;
> - }
> -}
> -
> -static uint32_t ht_lookup_and_upsert(HTEntry *ht, const AVCRC *hash_ctx,
> - uint32_t key, uint32_t pos)
> -{
> - uint32_t ret = -1;
> - size_t hash = av_crc(hash_ctx, 0, (uint8_t*)&key, 4) % LOOKBACK_HT_ELEMS;
> - for (size_t i = hash; i < hash + LOOKBACK_HT_ELEMS; i++) {
> - size_t wrapped_index = i % LOOKBACK_HT_ELEMS;
> - HTEntry *entry = &ht[wrapped_index];
> - if (entry->key == key || entry->pos == -1) {
> - ret = entry->pos;
> - entry->key = key;
> - entry->pos = pos;
> - break;
> - }
> - }
> - return ret;
> -}
> -
> -static void ht_delete(HTEntry *ht, const AVCRC *hash_ctx,
> - uint32_t key, uint32_t pos)
> -{
> - HTEntry *removed_entry = NULL;
> - size_t removed_hash;
> - size_t hash = av_crc(hash_ctx, 0, (uint8_t*)&key, 4) % LOOKBACK_HT_ELEMS;
> -
> - for (size_t i = hash; i < hash + LOOKBACK_HT_ELEMS; i++) {
> - size_t wrapped_index = i % LOOKBACK_HT_ELEMS;
> - HTEntry *entry = &ht[wrapped_index];
> - if (entry->pos == -1)
> - return;
> - if (removed_entry) {
> - size_t candidate_hash = av_crc(hash_ctx, 0, (uint8_t*)&entry->key, 4) % LOOKBACK_HT_ELEMS;
> - if ((wrapped_index > removed_hash && (candidate_hash <= removed_hash || candidate_hash > wrapped_index)) ||
> - (wrapped_index < removed_hash && (candidate_hash <= removed_hash && candidate_hash > wrapped_index))) {
> - *removed_entry = *entry;
> - entry->pos = -1;
> - removed_entry = entry;
> - removed_hash = wrapped_index;
> - }
> - } else if (entry->key == key) {
> - if (entry->pos <= pos) {
> - entry->pos = -1;
> - removed_entry = entry;
> - removed_hash = wrapped_index;
> - } else {
> - return;
> - }
> - }
> - }
> -}
> -
> typedef struct DXVEncContext {
> AVClass *class;
>
> @@ -123,10 +60,8 @@ typedef struct DXVEncContext {
> enum DXVTextureFormat tex_fmt;
> int (*compress_tex)(AVCodecContext *avctx);
>
> - const AVCRC *crc_ctx;
> -
> - HTEntry color_lookback_ht[LOOKBACK_HT_ELEMS];
> - HTEntry lut_lookback_ht[LOOKBACK_HT_ELEMS];
> + AVHashtableContext color_ht;
> + AVHashtableContext lut_ht;
> } DXVEncContext;
>
> /* Converts an index offset value to a 2-bit opcode and pushes it to a stream.
> @@ -161,27 +96,32 @@ static int dxv_compress_dxt1(AVCodecContext *avctx)
> DXVEncContext *ctx = avctx->priv_data;
> PutByteContext *pbc = &ctx->pbc;
> uint32_t *value;
> - uint32_t color, lut, idx, color_idx, lut_idx, prev_pos, state = 16, pos = 2, op = 0;
> + uint32_t color, lut, idx, color_idx, lut_idx, prev_pos, state = 16, pos = 0, op = 0;
>
> - ht_init(ctx->color_lookback_ht);
> - ht_init(ctx->lut_lookback_ht);
> + av_hashtable_clear(&ctx->color_ht);
> + av_hashtable_clear(&ctx->lut_ht);
>
> bytestream2_put_le32(pbc, AV_RL32(ctx->tex_data));
> + av_hashtable_set(&ctx->color_ht, ctx->tex_data, &pos);
> + pos++;
> bytestream2_put_le32(pbc, AV_RL32(ctx->tex_data + 4));
> -
> - ht_lookup_and_upsert(ctx->color_lookback_ht, ctx->crc_ctx, AV_RL32(ctx->tex_data), 0);
> - ht_lookup_and_upsert(ctx->lut_lookback_ht, ctx->crc_ctx, AV_RL32(ctx->tex_data + 4), 1);
> + av_hashtable_set(&ctx->lut_ht, ctx->tex_data + 4, &pos);
> + pos++;
>
> while (pos + 2 <= ctx->tex_size / 4) {
> idx = 0;
> + color_idx = 0;
> + lut_idx = 0;
>
> color = AV_RL32(ctx->tex_data + pos * 4);
> - prev_pos = ht_lookup_and_upsert(ctx->color_lookback_ht, ctx->crc_ctx, color, pos);
> - color_idx = prev_pos != -1 ? pos - prev_pos : 0;
> + if (av_hashtable_get(&ctx->color_ht, &color, &prev_pos))
> + color_idx = pos - prev_pos;
> + av_hashtable_set(&ctx->color_ht, &color, &pos);
> +
> if (pos >= LOOKBACK_WORDS) {
> uint32_t old_pos = pos - LOOKBACK_WORDS;
> - uint32_t old_color = AV_RL32(ctx->tex_data + old_pos * 4);
> - ht_delete(ctx->color_lookback_ht, ctx->crc_ctx, old_color, old_pos);
> + if (av_hashtable_get(&ctx->color_ht, ctx->tex_data + old_pos * 4, &prev_pos) && prev_pos <= old_pos)
> + av_hashtable_delete(&ctx->color_ht, ctx->tex_data + old_pos * 4);
> }
> pos++;
>
> @@ -190,13 +130,14 @@ static int dxv_compress_dxt1(AVCodecContext *avctx)
> idx = color_idx;
> } else {
> idx = 0;
> - prev_pos = ht_lookup_and_upsert(ctx->lut_lookback_ht, ctx->crc_ctx, lut, pos);
> - lut_idx = prev_pos != -1 ? pos - prev_pos : 0;
> + if (av_hashtable_get(&ctx->lut_ht, &lut, &prev_pos))
> + lut_idx = pos - prev_pos;
> + av_hashtable_set(&ctx->lut_ht, &lut, &pos);
> }
> if (pos >= LOOKBACK_WORDS) {
> uint32_t old_pos = pos - LOOKBACK_WORDS;
> - uint32_t old_lut = AV_RL32(ctx->tex_data + old_pos * 4);
> - ht_delete(ctx->lut_lookback_ht, ctx->crc_ctx, old_lut, old_pos);
> + if (av_hashtable_get(&ctx->lut_ht, ctx->tex_data + old_pos * 4, &prev_pos) && prev_pos <= old_pos)
> + av_hashtable_delete(&ctx->lut_ht, ctx->tex_data + old_pos * 4);
> }
> pos++;
>
> @@ -298,10 +239,15 @@ static av_cold int dxv_init(AVCodecContext *avctx)
> return AVERROR(ENOMEM);
> }
>
> - ctx->crc_ctx = av_crc_get_table(AV_CRC_32_IEEE);
> - if (!ctx->crc_ctx) {
> - av_log(avctx, AV_LOG_ERROR, "Could not initialize CRC table.\n");
> - return AVERROR_BUG;
> + ret = av_hashtable_init(&ctx->color_ht, sizeof(uint32_t), sizeof(uint32_t), LOOKBACK_HT_ELEMS);
> + if (ret < 0) {
> + av_log(avctx, AV_LOG_ERROR, "Could not initialize color lookback table.\n");
> + return ret;
> + }
> + ret = av_hashtable_init(&ctx->lut_ht, sizeof(uint32_t), sizeof(uint32_t), LOOKBACK_HT_ELEMS);
> + if (ret < 0) {
> + av_log(avctx, AV_LOG_ERROR, "Could not initialize LUT lookback table.\n");
These av_logs are pointless.
> + return ret;
> }
>
> return 0;
> @@ -313,6 +259,9 @@ static av_cold int dxv_close(AVCodecContext *avctx)
>
> av_freep(&ctx->tex_data);
>
> + av_hashtable_destroy(&ctx->color_ht);
> + av_hashtable_destroy(&ctx->lut_ht);
> +
> return 0;
> }
>
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