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Implement SIMD for YUYV to grayscale conversion

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Harshit-Dhanwalkar 2026-05-24 18:46:17 +05:30
parent 8a79d2fece
commit 509554ba1d
2 changed files with 27 additions and 5 deletions
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3
C/Makefile
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@ -1,7 +1,8 @@
CC = gcc
CFLAGS = -Wall -Wextra -O2 -Iinclude
LDFLAGS = -lm
LDFLAGS += -lpthread
LDFLAGS += -lpthread # Multi-threaded capture-render, pthreads producer/consumer
LDFLAGS += -msse4.1 # SIMD - SSE2 for the YUYV to gray conversion
SRCDIR = src
INCDIR = include

29
C/src/capture.c
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@ -10,6 +10,7 @@
#include <sys/mman.h>
#include <sys/select.h>
#include <unistd.h>
#include <immintrin.h>
int webcam_init(webcam_t *cam, const char *device, int width, int height) {
// Open device (non‑blocking for select usage)
@ -97,16 +98,36 @@ int webcam_wait_frame(webcam_t *cam, int timeout_ms) {
return 0;
}
void yuyv_to_gray_simd(const uint8_t *yuyv, uint8_t *gray, int n) {
// Mask to extract every even byte (Y samples)
__m128i mask = _mm_set1_epi16(0x00FF);
int i = 0;
for (; i + 16 <= n; i += 16) {
// Load 32 bytes of YUYV (= 16 pixels)
__m128i lo = _mm_loadu_si128((__m128i *)(yuyv + i*2));
__m128i hi = _mm_loadu_si128((__m128i *)(yuyv + i*2 + 16));
// low byte of each 16-bit word (the Y sample)
lo = _mm_and_si128(lo, mask);
hi = _mm_and_si128(hi, mask);
// Pack 16-bit
__m128i result = _mm_packus_epi16(lo, hi);
_mm_storeu_si128((__m128i *)(gray + i), result);
}
for (; i < n; i++) gray[i] = yuyv[i * 2]; // scalar tail
}
int webcam_capture_frame(webcam_t *cam, uint8_t *gray_buffer) {
// Dequeue buffer
struct v4l2_buffer buf = cam->buf_info;
if (ioctl(cam->fd, VIDIOC_DQBUF, &buf) < 0) return -1;
// Convert YUYV -> grayscale (Y component)
uint8_t *yuyv = (uint8_t *)cam->buffer;
for (int i = 0, j = 0; i < cam->width * cam->height * 2; i += 2, j++) {
gray_buffer[j] = yuyv[i];
}
// uint8_t *yuyv = (uint8_t *)cam->buffer;
// for (int i = 0, j = 0; i < cam->width * cam->height * 2; i += 2, j++) {
// gray_buffer[j] = yuyv[i];
// }
int total_pixels = cam->width * cam->height;
yuyv_to_gray_simd((uint8_t *)cam->buffer, gray_buffer, total_pixels);
// Store updated buffer info for requeue
cam->buf_info = buf;