Fix shift inside if constexpr

AntoinePrv · AntoinePrv · commit 3425fd0f1f73 · 2025-11-19T13:56:54.000+01:00
diff --git a/include/xsimd/arch/xsimd_avx2.hpp b/include/xsimd/arch/xsimd_avx2.hpp
@@ -181,7 +181,8 @@ namespace xsimd
             static_assert(shift < bits, "Shift must be less than the number of bits in T");
             XSIMD_IF_CONSTEXPR(sizeof(T) == 1)
             {
-                constexpr uint8_t mask8 = static_cast<uint8_t>(~0u << shift);
+                // TODO(C++17): without `if constexpr` we must ensure the compile-time shift does not overflow
+                constexpr uint8_t mask8 = static_cast<uint8_t>(sizeof(T) == 1 ? (~0u << shift) : 0);
                 __m256i const mask = _mm256_set1_epi8(mask8);
                 return _mm256_and_si256(_mm256_slli_epi16(self, shift), mask);
             }
@@ -314,7 +315,8 @@ namespace xsimd
             {
                 XSIMD_IF_CONSTEXPR(sizeof(T) == 1)
                 {
-                    constexpr uint8_t mask8 = static_cast<uint8_t>((1u << shift) - 1u);
+                    // TODO(C++17): without `if constexpr` we must ensure the compile-time shift does not overflow
+                    constexpr uint8_t mask8 = static_cast<uint8_t>(sizeof(T) == 1 ? ((1u << shift) - 1u) : 0);
                     __m256i const mask = _mm256_set1_epi8(mask8);
                     return _mm256_and_si256(_mm256_srli_epi16(self, shift), mask);
                 }

Original file line number	Diff line number	Diff line change
`@@ -181,7 +181,8 @@ namespace xsimd`
`181`	`181`	`static_assert(shift < bits, "Shift must be less than the number of bits in T");`
`182`	`182`	`XSIMD_IF_CONSTEXPR(sizeof(T) == 1)`
`183`	`183`	`{`
`184`		`- constexpr uint8_t mask8 = static_cast<uint8_t>(~0u << shift);`
	`184`	+ // TODO(C++17): without `if constexpr` we must ensure the compile-time shift does not overflow
	`185`	`+ constexpr uint8_t mask8 = static_cast<uint8_t>(sizeof(T) == 1 ? (~0u << shift) : 0);`
`185`	`186`	`__m256i const mask = _mm256_set1_epi8(mask8);`
`186`	`187`	`return _mm256_and_si256(_mm256_slli_epi16(self, shift), mask);`
`187`	`188`	`}`
`@@ -314,7 +315,8 @@ namespace xsimd`
`314`	`315`	`{`
`315`	`316`	`XSIMD_IF_CONSTEXPR(sizeof(T) == 1)`
`316`	`317`	`{`
`317`		`- constexpr uint8_t mask8 = static_cast<uint8_t>((1u << shift) - 1u);`
	`318`	+ // TODO(C++17): without `if constexpr` we must ensure the compile-time shift does not overflow
	`319`	`+ constexpr uint8_t mask8 = static_cast<uint8_t>(sizeof(T) == 1 ? ((1u << shift) - 1u) : 0);`
`318`	`320`	`__m256i const mask = _mm256_set1_epi8(mask8);`
`319`	`321`	`return _mm256_and_si256(_mm256_srli_epi16(self, shift), mask);`
`320`	`322`	`}`