Add SIMD comment skipping

1 files changed, 112 insertions, 0 deletions

diff --git a/c/simd-comment-skipping/skpcmnt.c b/c/simd-comment-skipping/skpcmnt.c
new file mode 100644
index 0000000..8a31544
--- /dev/null
+++ b/c/simd-comment-skipping/skpcmnt.c
@@ -0,0 +1,112 @@
+#define _GNU_SOURCE
+#include <sys/stat.h>
+
+#include <err.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+#include <x86intrin.h>
+
+#include <bsd/stdlib.h>
+
+#define MIN(x, y) ((x) < (y) ? (x) : (y))
+
+static char *readfile(const char *, size_t *);
+
+static bool
+skpcmnt(const char **ptr, const char *end)
+{
+	int nst = 0;
+	const char *p = *ptr, needles[] = {'/', '*', 0, 0, 0, 0, 0, 0,
+	                                   0,   0,   0, 0, 0, 0, 0, 0};
+	const __m128i set = _mm_loadu_si128((const __m128i *)needles);
+
+	while (p < end) {
+		ptrdiff_t len = end - p;
+		size_t blksz = MIN(len, 16);
+		__m128i blk = _mm_loadu_si128((const __m128i *)p);
+		int off = _mm_cmpestri(set, 2, blk, blksz, _SIDD_CMP_EQUAL_ANY);
+
+		if (off == 16) {
+			p += 16;
+			continue;
+		}
+
+		if (p[off] == '*' && p[off + 1] == '/') {
+			p += off + 2;
+			if (--nst == 0) {
+				*ptr = p;
+				return true;
+			}
+		} else if (p[off] == '/' && p[off + 1] == '*') {
+			p += off + 2;
+			nst++;
+		} else
+			p += off + 1;
+	}
+
+	return false;
+}
+
+int
+main(int argc, char **argv)
+{
+	if (argc != 2) {
+		fprintf(stderr, "Usage: %s file\n", getprogname());
+		exit(EXIT_FAILURE);
+	}
+
+	size_t len;
+	int rv = EXIT_SUCCESS;
+	const char *beg = readfile(argv[1], &len);
+	const char *end = beg + len;
+
+	clock_t tmbeg = clock();
+	while ((beg = memmem(beg, end - beg, "/*", 2)) != NULL) {
+		if (!skpcmnt((const char **)&beg, end)) {
+			warnx("Unterminated comment!");
+			rv = EXIT_FAILURE;
+			break;
+		}
+	}
+	clock_t tmend = clock();
+	printf("Elapsed time: %.3fs\n", (double)(tmend - tmbeg) / CLOCKS_PER_SEC);
+
+	return rv;
+}
+
+char *
+readfile(const char *filename, size_t *n)
+{
+	int fd = open(filename, O_RDONLY);
+	if (fd == -1)
+		err(1, "open: %s", filename);
+
+	struct stat sb;
+	if (fstat(fd, &sb) == -1)
+		err(1, "fstat: %s", filename);
+
+	char *p = malloc(sb.st_size + 4);
+	if (p == NULL)
+		err(1, "malloc");
+
+	ssize_t nr;
+	for (size_t off = 0; (nr = read(fd, p + off, sb.st_blksize)) > 0; off += nr)
+		;
+	if (nr == -1)
+		err(1, "read: %s", filename);
+
+	p[sb.st_size + 0] =
+	p[sb.st_size + 1] =
+	p[sb.st_size + 2] =
+	p[sb.st_size + 3] = 0;
+
+	*n = sb.st_size;
+	close(fd);
+	return p;
+}