Fix horizontal max for uchar

Fixes: VcDevel#349

Author: bernhardmgruber

Vc/sse/detail.h

@@ -764,9 +764,9 @@ Vc_INTRINSIC  schar max(__m128i a,  schar) {
     return std::max(schar(_mm_cvtsi128_si32(a) >> 8), schar(_mm_cvtsi128_si32(a)));
 }
 Vc_INTRINSIC  uchar max(__m128i a,  uchar) {
-    a = max(a, _mm_shuffle_epi32(a, _MM_SHUFFLE(1, 0, 3, 2)), schar());
-    a = max(a, _mm_shufflelo_epi16(a, _MM_SHUFFLE(1, 0, 3, 2)), schar());
-    a = max(a, _mm_shufflelo_epi16(a, _MM_SHUFFLE(1, 1, 1, 1)), schar());
+    a = max(a, _mm_shuffle_epi32(a, _MM_SHUFFLE(1, 0, 3, 2)), uchar());
+    a = max(a, _mm_shufflelo_epi16(a, _MM_SHUFFLE(1, 0, 3, 2)), uchar());
+    a = max(a, _mm_shufflelo_epi16(a, _MM_SHUFFLE(1, 1, 1, 1)), uchar());
     return std::max((_mm_cvtsi128_si32(a) >> 8) & 0xff, _mm_cvtsi128_si32(a) & 0xff);
 }
 

tests/arithmetics.cpp

@@ -472,6 +472,13 @@ TEST_TYPES(Vec, testMax, AllVectors)
     }
 }
 
+// Tests issue: https://github.com/VcDevel/Vc/issues/349
+TEST(Vec, maxChar) {
+    uint8_t a[64]{0, 10, 250};
+    COMPARE(Vc::schar_v((signed char*)a).max() == 10);
+    COMPARE(Vc::char_v(a).max() == 250);
+}
+
 // testProduct{{{1
 TEST_TYPES(Vec, testProduct, AllVectors)
 {