Update quantize_row_q4_0 for Arm NEON

Untested

Author: unbounded

ggml.c

@@ -759,19 +759,24 @@ static void quantize_row_q4_0(const float * restrict x, void * restrict vy, int
 #elif __ARM_NEON
     for (int i = 0; i < nb; i++) {
         float32x4_t srcv [8];
-        float32x4_t asrcv[8];
-        float32x4_t amaxv[8];
+        float32x4_t maxv[8];
+        float32x4_t minv[8];
 
         for (int l = 0; l < 8; l++) srcv[l]  = vld1q_f32(x + i*32 + 4*l);
-        for (int l = 0; l < 8; l++) asrcv[l] = vabsq_f32(srcv[l]);
 
-        for (int l = 0; l < 4; l++) amaxv[2*l] = vmaxq_f32(asrcv[2*l], asrcv[2*l+1]);
-        for (int l = 0; l < 2; l++) amaxv[4*l] = vmaxq_f32(amaxv[4*l], amaxv[4*l+2]);
-        for (int l = 0; l < 1; l++) amaxv[8*l] = vmaxq_f32(amaxv[8*l], amaxv[8*l+4]);
+        for (int l = 0; l < 4; l++) maxv[2*l] = vmaxq_f32(srcv[2*l], srcv[2*l+1]);
+        for (int l = 0; l < 2; l++) maxv[4*l] = vmaxq_f32(maxv[4*l], maxv[4*l+2]);
+        for (int l = 0; l < 1; l++) maxv[8*l] = vmaxq_f32(maxv[8*l], maxv[8*l+4]);
 
-        const float amax = vmaxvq_f32(amaxv[0]);
+        for (int l = 0; l < 4; l++) minv[2*l] = vminq_f32(srcv[2*l], srcv[2*l+1]);
+        for (int l = 0; l < 2; l++) minv[4*l] = vminq_f32(minv[4*l], minv[4*l+2]);
+        for (int l = 0; l < 1; l++) minv[8*l] = vminq_f32(minv[8*l], minv[8*l+4]);
 
-        const float d = amax / ((1 << 3) - 1);
+        const float max = vmaxvq_f32(maxv[0]);
+        const float min = vminvq_f32(minv[0]);
+
+        const float magnitude = max >= fabsf(min) ? max : min;
+        const float d = magnitude / -8;
         const float id = d ? 1.0f/d : 0.0f;
 
         y[i].d = d;
@@ -780,9 +785,10 @@ static void quantize_row_q4_0(const float * restrict x, void * restrict vy, int
             const float32x4_t v  = vmulq_n_f32(srcv[l], id);
             const float32x4_t vf = vaddq_f32(v, vdupq_n_f32(8.5f));
             const int32x4_t   vi = vcvtq_s32_f32(vf);
+            const int32x4     vc = vminq_u32(vi, vdupq_n_u32(15));
 
-            y[i].qs[2*l + 0] = vgetq_lane_s32(vi, 0) | (vgetq_lane_s32(vi, 1) << 4);
-            y[i].qs[2*l + 1] = vgetq_lane_s32(vi, 2) | (vgetq_lane_s32(vi, 3) << 4);
+            y[i].qs[2*l + 0] = vgetq_lane_s32(vc, 0) | (vgetq_lane_s32(vc, 1) << 4);
+            y[i].qs[2*l + 1] = vgetq_lane_s32(vc, 2) | (vgetq_lane_s32(vc, 3) << 4);
         }
     }
 #elif defined(__AVX2__)