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Fix GCC module build and MSVC C4127 in the json_view SIMD code

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GCC ignores the target attribute in modules, so the SSSE3 dispatch is
disabled for the module interface (the check stays portable, SSE2 is kept).
Make the 8-vs-16 byte unrolling condition in scan_string_run a
preprocessor/template split to avoid a constant condition (C4127).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-10-08 16:23:21 +02:00
1 parent ad715372bf
commit 9c7eb12918
5 files changed
+20 -4
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single_include/nlohmann/json_view.hpp
+7 -2
View File
@@ -439,6 +439,9 @@ NLOHMANN_JSON_NAMESPACE_END
// used where the CPU has SSSE3 (all x86-64 CPUs since about 2011), else the
// portable check. JSON_VIEW_USE_SSSE3 skips the CPU check (for code compiled
// for SSSE3 anyway); JSON_VIEW_NO_SIMD selects the portable code.
// NLOHMANN_VIEW_NO_TARGET_ATTRIBUTE (set by the GCC module interface, where GCC
// ignores the target attribute and then rejects the SSSE3 intrinsics) keeps the
// check portable without disabling the SSE2 code.
#if !defined(JSON_VIEW_NO_SIMD) && defined(__aarch64__) && (defined(__GNUC__) || defined(__clang__)) && NLOHMANN_VIEW_LITTLE_ENDIAN
#include <arm_neon.h>
#define NLOHMANN_VIEW_NEON 1
@@ -457,7 +460,7 @@ NLOHMANN_JSON_NAMESPACE_END
#else
#define NLOHMANN_VIEW_SSSE3 0 // NOLINT(cppcoreguidelines-macro-to-enum,modernize-macro-to-enum)
#endif
#if NLOHMANN_VIEW_SSE2 && !NLOHMANN_VIEW_SSSE3 && ((defined(__clang__) && __clang_major__ >= 4) || (defined(__GNUC__) && !defined(__clang__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9))))
#if NLOHMANN_VIEW_SSE2 && !NLOHMANN_VIEW_SSSE3 && !defined(NLOHMANN_VIEW_NO_TARGET_ATTRIBUTE) && ((defined(__clang__) && __clang_major__ >= 4) || (defined(__GNUC__) && !defined(__clang__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9))))
// (GCC before 4.9 has no SSSE3 intrinsics without -mssse3)
#include <cpuid.h>
#include <tmmintrin.h>
@@ -815,7 +818,9 @@ NLOHMANN_VIEW_ALWAYS_INLINE const unsigned char* scan_string_run(const unsigned
#define NLOHMANN_VIEW_STEP(i) if (NLOHMANN_VIEW_LIKELY(plain[p[i]] != 0)) {} else { p += (i); goto stop; }
NLOHMANN_VIEW_STEP(0) NLOHMANN_VIEW_STEP(1) NLOHMANN_VIEW_STEP(2) NLOHMANN_VIEW_STEP(3)
NLOHMANN_VIEW_STEP(4) NLOHMANN_VIEW_STEP(5) NLOHMANN_VIEW_STEP(6) NLOHMANN_VIEW_STEP(7)
if (!Value || !NLOHMANN_VIEW_VECTOR)
#if NLOHMANN_VIEW_VECTOR
if (!Value) // (a plain `!Value || !NLOHMANN_VIEW_VECTOR` is a constant condition for MSVC, C4127)
#endif
{
NLOHMANN_VIEW_STEP(8) NLOHMANN_VIEW_STEP(9) NLOHMANN_VIEW_STEP(10) NLOHMANN_VIEW_STEP(11)
NLOHMANN_VIEW_STEP(12) NLOHMANN_VIEW_STEP(13) NLOHMANN_VIEW_STEP(14) NLOHMANN_VIEW_STEP(15)