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encode: optimize image window bits #206

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encode: optimize image window bits #206

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b239513
encode: optimize image window bits
randy408 Feb 2, 2022
a03945d
disable deflate window bits optimization for miniz
randy408 Feb 3, 2022
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25 changes: 25 additions & 0 deletions spng/spng.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1161,6 +1161,19 @@ static int discard_chunk_bytes(spng_ctx *ctx, uint32_t bytes)
return 0;
}

static int minimum_window_bits(size_t size)
{
if(size > 16384) return 15;
else if(size > 8192) return 14;
else if(size > 4096) return 13;
else if(size > 2048) return 12;
else if(size > 1024) return 11;
else if(size > 512) return 10;
else if(size > 256) return 9;

return 8;
}

static int spng__inflate_init(spng_ctx *ctx, int window_bits)
{
if(ctx->zstream.state) inflateEnd(&ctx->zstream);
Expand Down Expand Up @@ -4788,6 +4801,18 @@ int spng_encode_image(spng_ctx *ctx, const void *img, size_t len, int fmt, int f
ctx->image_options.strategy = Z_DEFAULT_STRATEGY;
}

#ifndef SPNG_USE_MINIZ
if(ctx->image_size && spng__optimize(SPNG_IMG_WINDOW_BITS))
{
int window_bits = minimum_window_bits(ctx->image_size);

/* Avoid degrading compression factor (https://zlib.net/zlib_tech.html). */
if(window_bits < 15) window_bits++;

ctx->image_options.window_bits = window_bits;
}
#endif

ret = spng__deflate_init(ctx, &ctx->image_options);
if(ret) return encode_err(ctx, ret);

Expand Down