ggml : add AVX2 implementation of quantize_row_q4_1 (#515)

* Add AVX2 implementation of quantize_row_q4_1

* Actually use AVX2

* Make quantize_row_q4_1 static

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

ggml.c

@@ -688,7 +688,7 @@ static void quantize_row_q4_0(const float * restrict x, void * restrict vy, int
 #endif
 }
 
-static void quantize_row_q4_1(const float * restrict x, void * restrict vy, int k) {
+static void quantize_row_q4_1_reference(const float * restrict x, void * restrict vy, int k) {
     assert(k % QK == 0);
     const int nb = k / QK;
 
@@ -729,6 +729,93 @@ static void quantize_row_q4_1(const float * restrict x, void * restrict vy, int
     }
 }
 
+static void quantize_row_q4_1(const float * restrict x, void * restrict vy, int k) {
+    assert(k % QK == 0);
+
+#if defined(__AVX2__)
+    const int nb = k / QK;
+
+    block_q4_1 * restrict y = vy;
+
+    for (int i = 0; i < nb; i++) {
+        // Load elements into 4 AVX vectors
+        __m256 v0 = _mm256_loadu_ps( x );
+        __m256 v1 = _mm256_loadu_ps( x + 8 );
+        __m256 v2 = _mm256_loadu_ps( x + 16 );
+        __m256 v3 = _mm256_loadu_ps( x + 24 );
+        x += 32;
+
+        // Compute max for the block
+        __m256 vmax;
+        vmax = _mm256_max_ps( v0, v1 );
+        vmax = _mm256_max_ps( vmax, v2 );
+        vmax = _mm256_max_ps( vmax, v3 );
+
+        __m128 max4 = _mm_max_ps( _mm256_extractf128_ps( vmax, 1 ), _mm256_castps256_ps128( vmax ) );
+        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 vmin;
+        vmin = _mm256_min_ps( v0, v1 );
+        vmin = _mm256_min_ps( vmin, v2 );
+        vmin = _mm256_min_ps( vmin, v3 );
+
+        __m128 min4 = _mm_min_ps( _mm256_extractf128_ps( vmin, 1 ), _mm256_castps256_ps128( vmin ) );
+        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 - minScalar) / ((1 << 4) - 1);
+        const float id = d ? 1.0f/d : 0.0f;
+
+        y[i].m = minScalar;
+        y[i].d = d;
+
+        // x = (x-min)*id
+        const __m256 mul = _mm256_set1_ps( id );
+        const __m256 off = _mm256_set1_ps( minScalar );
+        v0 = _mm256_mul_ps( _mm256_sub_ps( v0, off ), mul );
+        v1 = _mm256_mul_ps( _mm256_sub_ps( v1, off ), mul );
+        v2 = _mm256_mul_ps( _mm256_sub_ps( v2, off ), mul );
+        v3 = _mm256_mul_ps( _mm256_sub_ps( v3, off ), mul );
+
+        // Round to nearest integer
+        v0 = _mm256_round_ps( v0, _MM_ROUND_NEAREST );
+        v1 = _mm256_round_ps( v1, _MM_ROUND_NEAREST );
+        v2 = _mm256_round_ps( v2, _MM_ROUND_NEAREST );
+        v3 = _mm256_round_ps( v3, _MM_ROUND_NEAREST );
+
+        // Convert floats to integers
+        __m256i i0 = _mm256_cvtps_epi32( v0 );
+        __m256i i1 = _mm256_cvtps_epi32( v1 );
+        __m256i i2 = _mm256_cvtps_epi32( v2 );
+        __m256i i3 = _mm256_cvtps_epi32( v3 );
+
+        // Convert int32 to int16
+        i0 = _mm256_packs_epi32( i0, i1 );	// 0, 1, 2, 3,  8, 9, 10, 11,  4, 5, 6, 7, 12, 13, 14, 15
+        i2 = _mm256_packs_epi32( i2, i3 );	// 16, 17, 18, 19,  24, 25, 26, 27,  20, 21, 22, 23, 28, 29, 30, 31
+                                            // Convert int16 to int8
+        i0 = _mm256_packs_epi16( i0, i2 );	// 0, 1, 2, 3,  8, 9, 10, 11,  16, 17, 18, 19,  24, 25, 26, 27,  4, 5, 6, 7, 12, 13, 14, 15, 20, 21, 22, 23, 28, 29, 30, 31
+
+        // We got our precious signed bytes, but the order is now wrong
+        // These AVX2 pack instructions process 16-byte pieces independently
+        // The following instruction is fixing the order
+        const __m256i perm = _mm256_setr_epi32( 0, 4, 1, 5, 2, 6, 3, 7 );
+        i0 = _mm256_permutevar8x32_epi32( i0, perm );
+
+        // Compress the vector into 4 bit/value, and store
+        __m128i res = packNibbles( i0 );
+        _mm_storeu_si128( ( __m128i* )y[i].qs, res );
+    }
+#else
+    // scalar
+    quantize_row_q4_1_reference(x, vy, k);
+#endif
+}
+
 static void dequantize_row_q4_0(const void * restrict vx, float * restrict y, int k) {
     assert(k % QK == 0);
     const int nb = k / QK;
@@ -10135,7 +10222,7 @@ size_t ggml_quantize_q4_1(const float * src, void * dst, int n, int k, int64_t *
     for (int j = 0; j < n; j += k) {
         block_q4_1 * restrict y = (block_q4_1 *)dst + j/QK;
 
-        quantize_row_q4_1(src + j, y, k);
+        quantize_row_q4_1_reference(src + j, y, k);
 
         for (int i = 0; i < nb; i++) {
             for (int l = 0; l < QK; l += 2) {