Disable SIMD Huffman encoding by default w/ SIMDe

Referring to the discussions under #838 and #250, the Huffman encoding
SIMD modules perform worse with SIMD Everywhere than the equivalent
C/scalar modules.  wasm32 is like x32 in that it uses 32-bit pointers
and 64-bit registers, so we could address the regression with some
wasm32 engines by using a 64-bit Huffman bit buffer, but the C/scalar
modules would still perform better with Google's V8 engine.  Also, there
is no known way to address the regression with native code.

This commit default-disables SIMD Huffman encoding when libjpeg-turbo is
built with WITH_SIMDE and adds a new environment variable
(JSIMD_HUFFENC) to force-enable SIMD Huffman encoding for testing
purposes when it is default-disabled.

simd/arm/neon-compat.h.in

@@ -22,7 +22,6 @@
 #cmakedefine HAVE_VLD1_S16_X3
 #cmakedefine HAVE_VLD1_U16_X2
 #cmakedefine HAVE_VLD1Q_U8_X4
-#cmakedefine WITH_SIMDE
 
 #if defined(WITH_SIMDE) && !defined(__EMSCRIPTEN__)
 #define SIMDE_ENABLE_NATIVE_ALIASES

simd/jsimd.c

@@ -94,8 +94,13 @@ init_simd(j_common_ptr cinfo)
 #endif
   if (!GETENV_S(env, 2, "JSIMD_FORCENONE") && !strcmp(env, "1"))
     simd_support = 0;
+#ifdef WITH_SIMDE
+  if (!GETENV_S(env, 2, "JSIMD_HUFFENC") && !strcmp(env, "1"))
+    simd_huffman = 1;
+#else
   if (!GETENV_S(env, 2, "JSIMD_NOHUFFENC") && !strcmp(env, "1"))
     simd_huffman = 0;
+#endif
 #endif
 
   if (cinfo->is_decompressor) {

src/jcapimin.c

@@ -5,7 +5,7 @@
  * Copyright (C) 1994-1998, Thomas G. Lane.
  * Modified 2003-2010 by Guido Vollbeding.
  * libjpeg-turbo Modifications:
- * Copyright (C) 2022, 2024-2025, D. R. Commander.
+ * Copyright (C) 2022, 2024-2026, D. R. Commander.
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
  *
@@ -108,8 +108,10 @@ jpeg_CreateCompress(j_compress_ptr cinfo, int version, size_t structsize)
   memset(cinfo->master, 0, sizeof(my_comp_master));
 #ifdef WITH_SIMD
   cinfo->master->simd_support = JSIMD_UNDEFINED;
+#ifndef WITH_SIMDE
   cinfo->master->simd_huffman = 1;
 #endif
+#endif
 }
 
 

src/jconfigint.h.in

@@ -75,6 +75,8 @@
 
 #define SIMD_ARCHITECTURE  @SIMD_ARCHITECTURE@
 
+#cmakedefine WITH_SIMDE 0
+
 #endif
 
 #cmakedefine WITH_PROFILE

src/jdapimin.c

@@ -6,7 +6,7 @@
  * Lossless JPEG Modifications:
  * Copyright (C) 1999, Ken Murchison.
  * libjpeg-turbo Modifications:
- * Copyright (C) 2016, 2022, 2024-2025, D. R. Commander.
+ * Copyright (C) 2016, 2022, 2024-2026, D. R. Commander.
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
  *
@@ -101,8 +101,10 @@ jpeg_CreateDecompress(j_decompress_ptr cinfo, int version, size_t structsize)
   memset(cinfo->master, 0, sizeof(my_decomp_master));
 #ifdef WITH_SIMD
   cinfo->master->simd_support = JSIMD_UNDEFINED;
+#ifndef WITH_SIMDE
   cinfo->master->simd_huffman = 1;
 #endif
+#endif
 }