package/jpeg-turbo/0001-libspng-Really-remove-gamma-correction-code.patch

From 0da22762971551462cfad8f0b11cfb037472a4e8 Mon Sep 17 00:00:00 2001
From: DRC <information@libjpeg-turbo.org>
Date: Thu, 16 Jul 2026 12:09:54 -0400
Subject: [PATCH] libspng: Really remove gamma correction code

We really don't use it, and fpclassify() apparently introduces yet
another libm dependency in some cases (although I can't reproduce that.)

Fixes #904

Upstream: https://github.com/libjpeg-turbo/libjpeg-turbo/commit/0da22762971551462cfad8f0b11cfb037472a4e8

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
---
 src/spng/spng.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/src/spng/spng.c b/src/spng/spng.c
index 06249d68..aeadb67e 100644
--- a/src/spng/spng.c
+++ b/src/spng/spng.c
@@ -353,9 +353,12 @@ struct spng_ctx
     int widest_pass;
     int last_pass; /* last non-empty pass */
 
+#if 0 /* libjpeg-turbo: Eliminate unused gamma correction code, which
+         introduces an unwanted libm dependency */
     uint16_t *gamma_lut; /* points to either _lut8 or _lut16 */
     uint16_t *gamma_lut16;
     uint16_t gamma_lut8[256];
+#endif
     unsigned char trns_px[8];
     union spng__decode_plte decode_plte;
     struct spng_sbit decode_sb;
@@ -1742,6 +1745,8 @@ static uint16_t sample_to_target(uint16_t sample, unsigned bit_depth, unsigned s
     return sample;
 }
 
+#if 0 /* libjpeg-turbo: Eliminate unused gamma correction code, which
+         introduces an unwanted libm dependency */
 static inline void gamma_correct_row(unsigned char *row, uint32_t pixels, int fmt, const uint16_t *gamma_lut)
 {
     uint32_t i;
@@ -1785,6 +1790,7 @@ static inline void gamma_correct_row(unsigned char *row, uint32_t pixels, int fm
         }
     }
 }
+#endif
 
 /* Apply transparency to output row */
 static inline void trns_row(unsigned char *row,
@@ -3302,7 +3308,10 @@ int spng_decode_scanline(spng_ctx *ctx, void *out, size_t len)
     const struct spng_subimage *sub = ctx->subimage;
 
     const struct spng_ihdr *ihdr = &ctx->ihdr;
+#if 0 /* libjpeg-turbo: Eliminate unused gamma correction code, which
+         introduces an unwanted libm dependency */
     const uint16_t *gamma_lut = ctx->gamma_lut;
+#endif
     unsigned char *trns_px = ctx->trns_px;
     const struct spng_sbit *sb = &ctx->decode_sb;
     const struct spng_plte_entry *plte = ctx->decode_plte.rgba;
@@ -3529,7 +3538,10 @@ int spng_decode_scanline(spng_ctx *ctx, void *out, size_t len)
 
     if(f.do_scaling) scale_row(out, width, fmt, processing_depth, sb);
 
+#if 0 /* libjpeg-turbo: Eliminate unused gamma correction code, which
+         introduces an unwanted libm dependency */
     if(f.apply_gamma) gamma_correct_row(out, width, fmt, gamma_lut);
+#endif
 
     /* The previous scanline is always defiltered */
     void *t = ctx->prev_scanline;
@@ -3768,6 +3780,8 @@ int spng_decode_image(spng_ctx *ctx, void *out, size_t len, int fmt, int flags)
 
     /*if(f.same_layout && !flags && !f.interlaced) f.zerocopy = 1;*/
 
+#if 0 /* libjpeg-turbo: Eliminate unused gamma correction code, which
+         introduces an unwanted libm dependency */
     uint16_t *gamma_lut = NULL;
 
     if(f.apply_gamma)
@@ -3807,15 +3821,14 @@ int spng_decode_image(spng_ctx *ctx, void *out, size_t len, int fmt, int flags)
         unsigned i;
         for(i=0; i < lut_entries; i++)
         {
-#if 0 /* libjpeg-turbo: Eliminate libm dependency */
             float c = pow((float)i / max, exponent) * max;
-#endif
             float c = 0.0f;
             if(c > max) c = max;
 
             gamma_lut[i] = (uint16_t)c;
         }
     }
+#endif
 
     struct spng_sbit *sb = &ctx->decode_sb;
 
@@ -5000,7 +5013,10 @@ void spng_ctx_free(spng_ctx *ctx)
 
     if(!ctx->user_owns_out_png) spng__free(ctx, ctx->out_png);
 
+#if 0 /* libjpeg-turbo: Eliminate unused gamma correction code, which
+         introduces an unwanted libm dependency */
     spng__free(ctx, ctx->gamma_lut16);
+#endif
 
     spng__free(ctx, ctx->row_buf);
     spng__free(ctx, ctx->scanline_buf);
-- 
2.47.3