arm: optimize vec4 div with NEON

CREDITS

@@ -79,3 +79,7 @@ https://stackoverflow.com/a/57793352/2676533
 
 https://stackoverflow.com/questions/32536265/how-to-convert-mm-shuffle-ps-sse-intrinsic-to-neon-intrinsic
 http://github.com/microsoft/DirectXMath
+
+16. ARM NEON Div
+
+http://github.com/microsoft/DirectXMath

include/cglm/simd/arm.h

@@ -131,6 +131,23 @@ glmm_norm_inf(float32x4_t a) {
   return glmm_hmax(glmm_abs(a));
 }
 
+static inline
+float32x4_t
+glmm_div(float32x4_t a, float32x4_t b) {
+#if CGLM_ARM641
+  return vdivq_f32(a, b);
+#else
+  /* 2 iterations of Newton-Raphson refinement of reciprocal */
+  float32x4_t r0, r1;
+  r0 = vrecpeq_f32(b);
+  r1 = vrecpsq_f32(r0, b);
+  r0 = vmulq_f32(r1, r0);
+  r1 = vrecpsq_f32(r0, b);
+  r0 = vmulq_f32(r1, r0);
+  return vmulq_f32(a, r0);
+#endif
+}
+
 static inline
 float32x4_t
 glmm_fmadd(float32x4_t a, float32x4_t b, float32x4_t c) {

include/cglm/simd/x86.h

@@ -209,6 +209,12 @@ glmm_store3(float v[3], __m128 vx) {
   _mm_store_ss(&v[2], glmm_shuff1(vx, 2, 2, 2, 2));
 }
 
+static inline
+__m128
+glmm_div(__m128 a, __m128 b) {
+  return _mm_div_ps(a, b);
+}
+
 /* enable FMA macro for MSVC? */
 #if defined(_MSC_VER) && !defined(__FMA__) && defined(__AVX2__)
 #  define __FMA__ 1

include/cglm/vec4.h

@@ -473,8 +473,8 @@ glm_vec4_scale_as(vec4 v, float s, vec4 dest) {
 CGLM_INLINE
 void
 glm_vec4_div(vec4 a, vec4 b, vec4 dest) {
-#if defined( __SSE__ ) || defined( __SSE2__ )
-  glmm_store(dest, _mm_div_ps(glmm_load(a), glmm_load(b)));
+#if defined(CGLM_SIMD)
+  glmm_store(dest, glmm_div(glmm_load(a), glmm_load(b)));
 #else
   dest[0] = a[0] / b[0];
   dest[1] = a[1] / b[1];