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authorPedro F. Giffuni <pfg@FreeBSD.org>2021-05-31 01:48:38 +0000
committerPedro F. Giffuni <pfg@FreeBSD.org>2021-06-01 21:00:28 +0000
commita45843c8ed7fcc10c1f10d4346cc7b3c293c894b (patch)
tree91cf85f0a603b60a9d31721d98785ebf6b7cbb92 /lib/libc
parent0f86492b09ca82042166a41f6f21b2dbe4f4a464 (diff)
downloadsrc-a45843c8ed7fcc10c1f10d4346cc7b3c293c894b.tar.gz
src-a45843c8ed7fcc10c1f10d4346cc7b3c293c894b.zip
fread: improve performance for unbuffered reads
We can use the buffer passed to fread(3) directly in the FILE *. The buffer needs to be reset before each call to __srefill(). This preserves the expected behavior in all cases. The change was found originally in OpenBSD and later adopted by NetBSD. MFC after: 2 weeks Obtained from: OpenBSD (CVS 1.18) Differential Revision: https://reviews.freebsd.org/D30548
Diffstat (limited to 'lib/libc')
-rw-r--r--lib/libc/stdio/fread.c29
1 files changed, 29 insertions, 0 deletions
diff --git a/lib/libc/stdio/fread.c b/lib/libc/stdio/fread.c
index c12bcf1148b7..11f8d13f0caf 100644
--- a/lib/libc/stdio/fread.c
+++ b/lib/libc/stdio/fread.c
@@ -99,6 +99,35 @@ __fread(void * __restrict buf, size_t size, size_t count, FILE * __restrict fp)
fp->_r = 0;
total = resid;
p = buf;
+
+ /*
+ * If we're unbuffered we know that the buffer in fp is empty so
+ * we can read directly into buf. This is much faster than a
+ * series of one byte reads into fp->_nbuf.
+ */
+ if ((fp->_flags & __SNBF) != 0 && buf != NULL) {
+ while (resid > 0) {
+ /* set up the buffer */
+ fp->_bf._base = fp->_p = p;
+ fp->_bf._size = resid;
+
+ if (__srefill(fp)) {
+ /* no more input: return partial result */
+ count = (total - resid) / size;
+ break;
+ }
+ p += fp->_r;
+ resid -= fp->_r;
+ }
+
+ /* restore the old buffer (see __smakebuf) */
+ fp->_bf._base = fp->_p = fp->_nbuf;
+ fp->_bf._size = 1;
+ fp->_r = 0;
+
+ return (count);
+ }
+
while (resid > (r = fp->_r)) {
(void)memcpy((void *)p, (void *)fp->_p, (size_t)r);
fp->_p += r;