From: Nathan Moinvaziri <nathan@nathanm.com>
Date: Sat, 6 Dec 2025 15:55:07 +0000 (-0800)
Subject: Use __builtin_bitreverse16 in bi_reverse if available.
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=46ef5b645c27441323ed33ab07653a96d3ada0d1;p=thirdparty%2Fzlib-ng.git

Use __builtin_bitreverse16 in bi_reverse if available.
---

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5bb690607..39b0efe75 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -643,6 +643,24 @@ if(HAVE_BUILTIN_CTZLL)
 endif()
 set(CMAKE_REQUIRED_FLAGS)
 
+#
+# check for __builtin_bitreverse16() support in the compiler
+#
+set(CMAKE_REQUIRED_FLAGS ${ZNOLTOFLAG})
+check_c_source_compiles(
+    "int main(void) {
+        unsigned short val = 0x1234;
+        unsigned short test = __builtin_bitreverse16(val);
+        (void)test;
+        return 0;
+    }"
+    HAVE_BUILTIN_BITREVERSE16
+)
+if(HAVE_BUILTIN_BITREVERSE16)
+    add_definitions(-DHAVE_BUILTIN_BITREVERSE16)
+endif()
+set(CMAKE_REQUIRED_FLAGS)
+
 #
 # check for ptrdiff_t support
 #
diff --git a/configure b/configure
index 1aef2c367..5b95e37d6 100755
--- a/configure
+++ b/configure
@@ -1143,6 +1143,19 @@ else
     echo "Checking for __builtin_ctzll ... No." | tee -a configure.log
 fi
 
+# Check for __builtin_bitreverse16() support in compiler
+cat > $test.c << EOF
+unsigned short f(unsigned short x) { return __builtin_bitreverse16(x); }
+int main(void) { return 0; }
+EOF
+if try ${CC} ${CFLAGS} $test.c $LDSHAREDLIBC; then
+    echo "Checking for __builtin_bitreverse16 ... Yes." | tee -a configure.log
+    CFLAGS="$CFLAGS -DHAVE_BUILTIN_BITREVERSE16"
+    SFLAGS="$SFLAGS -DHAVE_BUILTIN_BITREVERSE16"
+else
+    echo "Checking for __builtin_bitreverse16 ... No." | tee -a configure.log
+fi
+
 check_avx2_intrinsics() {
     # Check whether compiler supports AVX2 intrinsics
     cat > $test.c << EOF
diff --git a/deflate_p.h b/deflate_p.h
index ecaad5c55..991c897a5 100644
--- a/deflate_p.h
+++ b/deflate_p.h
@@ -10,6 +10,7 @@
 #define DEFLATE_P_H
 
 #include "functable.h"
+#include "fallback_builtins.h"
 
 /* Forward declare common non-inlined functions declared in deflate.c */
 
@@ -127,13 +128,11 @@ Z_FORCEINLINE static void flush_pending_inline(PREFIX3(stream) *strm) {
 /* ===========================================================================
  * Reverse the first len bits of a code using bit manipulation
  */
-static inline uint16_t bi_reverse(unsigned code, int len) {
+Z_FORCEINLINE static uint16_t bi_reverse(unsigned code, int len) {
     /* code: the value to invert */
     /* len: its bit length */
     Assert(len >= 1 && len <= 15, "code length must be 1-15");
-#define bitrev8(b) \
-    (uint8_t)((((uint8_t)(b) * 0x80200802ULL) & 0x0884422110ULL) * 0x0101010101ULL >> 32)
-    return (bitrev8(code >> 8) | (uint16_t)bitrev8(code) << 8) >> (16 - len);
+    return __builtin_bitreverse16((uint16_t)code) >> (16 - len);
 }
 
 /* ===========================================================================
diff --git a/fallback_builtins.h b/fallback_builtins.h
index 8303508fa..89734eda4 100644
--- a/fallback_builtins.h
+++ b/fallback_builtins.h
@@ -12,7 +12,7 @@
  * If tzcnt instruction is not supported, the cpu will itself execute bsf instead.
  * Performance tzcnt/bsf is identical on Intel cpu, tzcnt is faster than bsf on AMD cpu.
  */
-static __forceinline int __builtin_ctz(unsigned int value) {
+Z_FORCEINLINE static int __builtin_ctz(unsigned int value) {
     Assert(value != 0, "Invalid input value: 0");
 # if defined(X86_FEATURES) && !(_MSC_VER < 1700)
     return (int)_tzcnt_u32(value);
@@ -28,7 +28,7 @@ static __forceinline int __builtin_ctz(unsigned int value) {
 /* This is not a general purpose replacement for __builtin_ctzll. The function expects that value is != 0.
  * Because of that assumption trailing_zero is not initialized and the return value is not checked.
  */
-static __forceinline int __builtin_ctzll(unsigned long long value) {
+Z_FORCEINLINE static int __builtin_ctzll(unsigned long long value) {
     Assert(value != 0, "Invalid input value: 0");
 # if defined(X86_FEATURES) && !(_MSC_VER < 1700)
     return (int)_tzcnt_u64(value);
@@ -44,4 +44,16 @@ static __forceinline int __builtin_ctzll(unsigned long long value) {
 #endif // Microsoft AMD64/IA64/x86/ARM/ARM64 test
 #endif // _MSC_VER & !clang
 
+#ifndef HAVE_BUILTIN_BITREVERSE16
+/* Bit reversal for 8-bit values using multiplication method */
+#define bitrev8(value) \
+    (uint8_t)((((uint8_t)(value) * 0x80200802ULL) & 0x0884422110ULL) * 0x0101010101ULL >> 32)
+
+/* General purpose bit reversal for 16-bit values */
+Z_FORCEINLINE static uint16_t __builtin_bitreverse16(uint16_t value) {
+    return ((bitrev8(value >> 8) | (uint16_t)bitrev8(value) << 8));
+}
+#define HAVE_BUILTIN_BITREVERSE16
+#endif
+
 #endif // include guard FALLBACK_BUILTINS_H