Update quantize_row_q4_0 for AVX/AVX2

Author: unbounded

ggml.c

@@ -642,22 +642,31 @@ static void quantize_row_q4_0(const float * restrict x, void * restrict vy, int
         __m256 v3 = _mm256_loadu_ps( x + 24 );
         x += 32;
 
-        // Compute max(abs(e)) for the block
-        const __m256 signBit = _mm256_set1_ps( -0.0f );
-        __m256 maxAbs = _mm256_andnot_ps( signBit, v0 );
-        maxAbs = _mm256_max_ps( maxAbs, _mm256_andnot_ps( signBit, v1 ) );
-        maxAbs = _mm256_max_ps( maxAbs, _mm256_andnot_ps( signBit, v2 ) );
-        maxAbs = _mm256_max_ps( maxAbs, _mm256_andnot_ps( signBit, v3 ) );
-
-        __m128 max4 = _mm_max_ps( _mm256_extractf128_ps( maxAbs, 1 ), _mm256_castps256_ps128( maxAbs ) );
+        // Compute max for the block
+        __m256 max  = _mm256_max_ps( v0, v1 );
+        __m256 maxTmp = _mm256_max_ps( v2, v3 );
+        max = _mm256_max_ps( max, maxTmp );
+
+        __m128 max4 = _mm_max_ps( _mm256_extractf128_ps( max, 1 ), _mm256_castps256_ps128( max ) );
         max4 = _mm_max_ps( max4, _mm_movehl_ps( max4, max4 ) );
         max4 = _mm_max_ss( max4, _mm_movehdup_ps( max4 ) );
         const float maxScalar = _mm_cvtss_f32( max4 );
 
+        // Compute min for the block
+        __m256 min  = _mm256_min_ps( v0, v1 );
+        __m256 minTmp = _mm256_min_ps( v2, v3 );
+        min = _mm256_min_ps( min, minTmp );
+
+        __m128 min4 = _mm_min_ps( _mm256_extractf128_ps( min, 1 ), _mm256_castps256_ps128( min ) );
+        min4 = _mm_min_ps( min4, _mm_movehl_ps( min4, min4 ) );
+        min4 = _mm_min_ss( min4, _mm_movehdup_ps( min4 ) );
+        const float minScalar = _mm_cvtss_f32( min4 );
+
         // Quantize these floats
-        const float d = maxScalar / 7.0f;
+        const float magnitude = maxScalar >= fabsf(minScalar) ? maxScalar : minScalar;
+        const float d = magnitude / -8.0f;
         y[i].d = d;
-        const float id = ( maxScalar != 0.0f ) ? 7.0f / maxScalar : 0.0f;
+        const float id = ( magnitude != 0.0f ) ? -8.0f / magnitude : 0.0f;
         const __m256 mul = _mm256_set1_ps( id );
 
         // Apply the multiplier
@@ -690,9 +699,11 @@ static void quantize_row_q4_0(const float * restrict x, void * restrict vy, int
         const __m256i perm = _mm256_setr_epi32( 0, 4, 1, 5, 2, 6, 3, 7 );
         i0 = _mm256_permutevar8x32_epi32( i0, perm );
 
-        // Apply offset to translate the range from [ -7 .. +7 ] into [ +1 .. +15 ]
+        // Apply offset and clamp to translate the range from [ -8 .. +8 ] into [ +0 .. +15 ]
         const __m256i off = _mm256_set1_epi8( 8 );
         i0 = _mm256_add_epi8( i0, off );
+        const __m256i maxNibble = _mm256_set1_epi8( 15 );
+        i0 = _mm256_min_epi8( i0, maxNibble );
 
         // Compress the vector into 4 bit/value, and store
         __m128i res = packNibbles( i0 );
@@ -707,22 +718,31 @@ static void quantize_row_q4_0(const float * restrict x, void * restrict vy, int
         __m256 v3 = _mm256_loadu_ps( x + 24 );
         x += 32;
 
-        // Compute max(abs(e)) for the block
-        const __m256 signBit = _mm256_set1_ps( -0.0f );
-        __m256 maxAbs = _mm256_andnot_ps( signBit, v0 );
-        maxAbs = _mm256_max_ps( maxAbs, _mm256_andnot_ps( signBit, v1 ) );
-        maxAbs = _mm256_max_ps( maxAbs, _mm256_andnot_ps( signBit, v2 ) );
-        maxAbs = _mm256_max_ps( maxAbs, _mm256_andnot_ps( signBit, v3 ) );
+        // Compute max for the block
+        __m256 max  = _mm256_max_ps( v0, v1 );
+        __m256 maxTmp = _mm256_max_ps( v2, v3 );
+        max = _mm256_max_ps( max, maxTmp );
 
-        __m128 max4 = _mm_max_ps( _mm256_extractf128_ps( maxAbs, 1 ), _mm256_castps256_ps128( maxAbs ) );
+        __m128 max4 = _mm_max_ps( _mm256_extractf128_ps( max, 1 ), _mm256_castps256_ps128( max ) );
         max4 = _mm_max_ps( max4, _mm_movehl_ps( max4, max4 ) );
         max4 = _mm_max_ss( max4, _mm_movehdup_ps( max4 ) );
         const float maxScalar = _mm_cvtss_f32( max4 );
 
+        // Compute min for the block
+        __m256 min  = _mm256_min_ps( v0, v1 );
+        __m256 minTmp = _mm256_min_ps( v2, v3 );
+        min = _mm256_min_ps( min, minTmp );
+
+        __m128 min4 = _mm_min_ps( _mm256_extractf128_ps( min, 1 ), _mm256_castps256_ps128( min ) );
+        min4 = _mm_min_ps( min4, _mm_movehl_ps( min4, min4 ) );
+        min4 = _mm_min_ss( min4, _mm_movehdup_ps( min4 ) );
+        const float minScalar = _mm_cvtss_f32( min4 );
+
         // Quantize these floats
-        const float d = maxScalar / 7.0f;
+        const float magnitude = maxScalar >= fabsf(minScalar) ? maxScalar : minScalar;
+        const float d = magnitude / -8.0f;
         y[i].d = d;
-        const float id = ( maxScalar != 0.0f ) ? 7.0f / maxScalar : 0.0f;
+        const float id = ( magnitude != 0.0f ) ? -8.0f / magnitude : 0.0f;
         const __m256 mul = _mm256_set1_ps( id );
 
         // Apply the multiplier
@@ -763,10 +783,13 @@ static void quantize_row_q4_0(const float * restrict x, void * restrict vy, int
         ni0 = _mm_packs_epi16( ni0, ni2 );
         ni4 = _mm_packs_epi16( ni4, ni6 );
 
-        // Apply offset to translate the range from [ -7 .. +7 ] into [ +1 .. +15 ]
-        const __m128i off = _mm_set1_epi8( 8);
+        // Apply offset and clamp to translate the range from [ -8 .. +8 ] into [ +0 .. +15 ]
+        const __m128i off = _mm_set1_epi8( 8 );
         ni0 = _mm_add_epi8( ni0, off );
         ni4 = _mm_add_epi8( ni4, off );
+        const __m128i maxNibble = _mm_set1_epi8( 15 );
+        ni0 = _mm_min_epi8( ni0, maxNibble );
+        ni4 = _mm_min_epi8( ni4, maxNibble );
 
         // Compress the vector into 4 bit/value, and store
         __m128i res = packNibbles( ni0, ni4 );