Only prefer POPCNT for 8-bit bit-counting on newer AMD CPUs

A lookup is likely faster everywhere else Ref #4
animetosho · Sep 25, 2017 · 7ae8661 · 7ae8661
1 parent eefc33c
commit 7ae8661
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Showing 3 changed files with 4 additions and 6 deletions.
diff --git a/src/common.h b/src/common.h
@@ -71,7 +71,6 @@
 #endif
 
 
-#ifndef __POPCNT__
 // table from http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetTable
 static const unsigned char BitsSetTable256[256] = 
 {
@@ -83,7 +82,6 @@ static const unsigned char BitsSetTable256[256] =
 #undef B4
 #undef B6
 };
-#endif
 
 
 

diff --git a/src/decoder.cc b/src/decoder.cc
@@ -281,7 +281,7 @@ size_t do_decode_sse(const unsigned char* src, unsigned char* dest, size_t len,
 			// all that's left is to 'compress' the data (skip over masked chars)
 #ifdef __SSSE3__
 			if(use_ssse3) {
-# ifdef __POPCNT__
+# if defined(__POPCNT__) && (defined(__tune_znver1__) || defined(__tune_btver2__))
 				unsigned char skipped = _mm_popcnt_u32(mask & 0xff);
 # else
 				unsigned char skipped = BitsSetTable256[mask & 0xff];
@@ -300,7 +300,7 @@ size_t do_decode_sse(const unsigned char* src, unsigned char* dest, size_t len,
 				STOREU_XMM(p, oData);
 
 				// increment output position
-# ifdef __POPCNT__
+# if defined(__POPCNT__) && !defined(__tune_btver1__)
 				p += XMM_SIZE - _mm_popcnt_u32(mask);
 # else
 				p += XMM_SIZE - skipped - BitsSetTable256[mask >> 8];

diff --git a/src/encoder.cc b/src/encoder.cc
@@ -260,7 +260,7 @@ static size_t do_encode_fast(int line_size, int* colOffset, const unsigned char*
 				data = _mm_add_epi8(data, shufMixMA);
 				data2 = _mm_add_epi8(data2, shufMixMB);
 				// store out
-#ifdef __POPCNT__
+#if defined(__POPCNT__) && (defined(__tune_znver1__) || defined(__tune_btver2__))
 				unsigned char shufALen = _mm_popcnt_u32(m1) + 8;
 				unsigned char shufBLen = _mm_popcnt_u32(m2) + 8;
 #else
@@ -652,7 +652,7 @@ size_t do_encode_fast2(int line_size, int* colOffset, const unsigned char* src,
 				data = _mm_add_epi8(data, shufMixMA);
 				data2 = _mm_add_epi8(data2, shufMixMB);
 				// store out
-#ifdef __POPCNT__
+#if defined(__POPCNT__) && (defined(__tune_znver1__) || defined(__tune_btver2__))
 				unsigned char shufALen = _mm_popcnt_u32(m1) + 8;
 				unsigned char shufBLen = _mm_popcnt_u32(m2) + 8;
 #else