Break up loop for numeric stability

ggml.c

@@ -1700,12 +1700,19 @@ inline static void ggml_vec_dot_q4_1(const int n, float * restrict s, const void
 #if defined(__AVX2__)
 #if QK == 32
     // Initialize accumulator with zeros
-    __m256 acc = _mm256_setzero_ps();
+    __m256 acc;
     // Accumulator for constant offsets
-    float acc_offset = 0.0f;
+    __m128 acc_offset;
 
+    int i = 0;
+#define LOOP_SPLITS 2
+#pragma GCC unroll 999
+    for(int j = 1; j <= LOOP_SPLITS; ++j) {
+    acc = _mm256_setzero_ps();
+    acc_offset = _mm_setzero_ps();
+    
     // Main loop
-    for (int i = 0; i < nb; ++i) {
+    for (; i < (j*nb)/LOOP_SPLITS; ++i) {
         const float * m0 = (const float *) (pm0 + i*bs);
         const float * m1 = (const float *) (pm1 + i*bs);
 
@@ -1756,14 +1763,17 @@ inline static void ggml_vec_dot_q4_1(const int n, float * restrict s, const void
         __m256i sumsi = _mm256_or_si256( xsumi, _mm256_slli_si256( ysumi, 4 ) );
         __m256  sums  = _mm256_cvtepi32_ps( sumsi );
 
+        // Apply the scales, and accumulate
+        // acc += d0*m1*x + d1*m0*y
+        acc = _mm256_fmadd_ps( cross_scales, sums, acc );
+
         // Convert int32_t to float
         __m256 p = _mm256_cvtepi32_ps( i32 );
-        // Apply the scale, and accumulate
-        // acc += d0*d1*x*y + d0*m1*x + d1*m0*y
+        // acc += d0*d1*x*y
         acc = _mm256_fmadd_ps( scale_01, p, acc );
-        acc = _mm256_fmadd_ps( cross_scales, sums, acc );
-        // acc_offset += m0*m1 (for each entry in the block)
-        acc_offset += (*m0)*(*m1);
+
+        // acc_offset += m0*m1 (avoid reloading from RAM)
+        acc_offset = _mm_fmadd_ss( _mm256_castps256_ps128( m0v ), _mm256_castps256_ps128( m1v ), acc_offset );
     }
 
     // Return horizontal sum of the acc vector
@@ -1772,7 +1782,8 @@ inline static void ggml_vec_dot_q4_1(const int n, float * restrict s, const void
     res = _mm_add_ps( res, _mm_movehl_ps( res, res ) );
     res = _mm_add_ss( res, _mm_movehdup_ps( res ) );
 
-    sumf = _mm_cvtss_f32( res ) + acc_offset * QK;
+    sumf += _mm_cvtss_f32( res ) + _mm_cvtss_f32( acc_offset )* QK;
+    }
 #else
 #error "not implemented for QK"
 #endif