Don't use vdotq_s32 if it's not available (#139)

* Don't use vdotq_s32 if it's not available

`dotprod` extensions aren't available on some ARM CPUs (e.g. Raspberry Pi 4), so check for them and only use them if they're available.

Reintroduces the code removed in 84d9015 if `__ARM_FEATURE_DOTPROD` isn't defined.

* Update ggml.c

---------

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

ggml.c

@@ -1359,8 +1359,8 @@ inline static void ggml_vec_dot_q4_0(const int n, float * restrict s, const void
         const int8x16_t v0_1hs = vsubq_s8(v0_1h, s8b);
         const int8x16_t v1_1hs = vsubq_s8(v1_1h, s8b);
 
+#if defined(__ARM_FEATURE_DOTPROD)
         // dot product into int16x8_t
-        // assume that vdotq_s32 is always available, if not, should check for __ARM_FEATURE_DOTPROD
         int32x4_t p_0 = vdotq_s32(vdupq_n_s32(0), v0_0ls, v1_0ls);
         int32x4_t p_1 = vdotq_s32(vdupq_n_s32(0), v0_1ls, v1_1ls);
 
@@ -1374,6 +1374,37 @@ inline static void ggml_vec_dot_q4_0(const int n, float * restrict s, const void
 #else
         sum0 += d0_0*d1_0*(vgetq_lane_s32(p_0, 0) + vgetq_lane_s32(p_0, 1) + vgetq_lane_s32(p_0, 2) + vgetq_lane_s32(p_0, 3));
         sum1 += d0_1*d1_1*(vgetq_lane_s32(p_1, 0) + vgetq_lane_s32(p_1, 1) + vgetq_lane_s32(p_1, 2) + vgetq_lane_s32(p_1, 3));
+#endif
+#else
+	    const int16x8_t pl0l = vmull_s8(vget_low_s8 (v0_0ls), vget_low_s8 (v1_0ls));
+        const int16x8_t pl0h = vmull_s8(vget_high_s8(v0_0ls), vget_high_s8(v1_0ls));
+
+        const int16x8_t ph0l = vmull_s8(vget_low_s8 (v0_0hs), vget_low_s8 (v1_0hs));
+        const int16x8_t ph0h = vmull_s8(vget_high_s8(v0_0hs), vget_high_s8(v1_0hs));
+
+        const int16x8_t pl1l = vmull_s8(vget_low_s8 (v0_1ls), vget_low_s8 (v1_1ls));
+        const int16x8_t pl1h = vmull_s8(vget_high_s8(v0_1ls), vget_high_s8(v1_1ls));
+
+        const int16x8_t ph1l = vmull_s8(vget_low_s8 (v0_1hs), vget_low_s8 (v1_1hs));
+        const int16x8_t ph1h = vmull_s8(vget_high_s8(v0_1hs), vget_high_s8(v1_1hs));
+
+        const int16x8_t pl_0 = vaddq_s16(pl0l, pl0h);
+        const int16x8_t ph_0 = vaddq_s16(ph0l, ph0h);
+
+        const int16x8_t pl_1 = vaddq_s16(pl1l, pl1h);
+        const int16x8_t ph_1 = vaddq_s16(ph1l, ph1h);
+
+        const int16x8_t p_0 = vaddq_s16(pl_0, ph_0);
+        const int16x8_t p_1 = vaddq_s16(pl_1, ph_1);
+
+        // scalar
+#if defined(__ARM_FEATURE_QRDMX)
+        sum0 += d0_0*d1_0*vaddvq_s16(p_0);
+        sum1 += d0_1*d1_1*vaddvq_s16(p_1);
+#else
+        sum0 += d0_0*d1_0*(vgetq_lane_s16(p_0, 0) + vgetq_lane_s16(p_0, 1) + vgetq_lane_s16(p_0, 2) + vgetq_lane_s16(p_0, 3) + vgetq_lane_s16(p_0, 4) + vgetq_lane_s16(p_0, 5) + vgetq_lane_s16(p_0, 6) + vgetq_lane_s16(p_0, 7));
+        sum1 += d0_1*d1_1*(vgetq_lane_s16(p_1, 0) + vgetq_lane_s16(p_1, 1) + vgetq_lane_s16(p_1, 2) + vgetq_lane_s16(p_1, 3) + vgetq_lane_s16(p_1, 4) + vgetq_lane_s16(p_1, 5) + vgetq_lane_s16(p_1, 6) + vgetq_lane_s16(p_1, 7));
+#endif
 #endif
     }