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Slightly better neon code. #3

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Slightly better neon code. #3

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16 changes: 9 additions & 7 deletions mandel_neon.c
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Original file line number Diff line number Diff line change
@@ -1,6 +1,13 @@
#include <arm_neon.h>
#include "mandel.h"

static inline int is_zero(uint32x4_t mask) {
uint64x2_t v64 = vreinterpretq_u64_u32(mask);
uint32x2_t v32 = vqmovn_u64(v64);
uint64x1_t result = vreinterpret_u64_u32(v32);
return result[0] == 0;
}

void
mandel_neon(unsigned char *image, const struct spec *s)
{
Expand All @@ -12,9 +19,7 @@ mandel_neon(unsigned char *image, const struct spec *s)
float32x4_t one = vdupq_n_f32(1);
float32x4_t iter_scale = vdupq_n_f32(1.0f / s->iterations);
float32x4_t depth_scale = vdupq_n_f32(s->depth - 1);
float32x4_t c0123; // {0.0f, 1.0f, 2.0f, 3.0f}
for (int i = 0; i < 4; i++)
c0123 = vsetq_lane_f32(i, c0123, i);
float32x4_t c0123 = {0.0f, 1.0f, 2.0f, 3.0f};

#pragma omp parallel for schedule(dynamic, 1)
for (int y = 0; y < s->height; y++) {
Expand Down Expand Up @@ -44,10 +49,7 @@ mandel_neon(unsigned char *image, const struct spec *s)
uint32x4_t mask = vcltq_f32(mag2, threshold);

/* Early bailout? */
if (vgetq_lane_u32(mask, 0) == 0 &&
vgetq_lane_u32(mask, 1) == 0 &&
vgetq_lane_u32(mask, 2) == 0 &&
vgetq_lane_u32(mask, 3) == 0)
if (is_zero(mask))
break;

/* Increment k */
Expand Down