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author | Pedro F. Giffuni <pfg@FreeBSD.org> | 2021-05-31 01:48:38 +0000 |
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committer | Pedro F. Giffuni <pfg@FreeBSD.org> | 2021-06-01 21:00:28 +0000 |
commit | a45843c8ed7fcc10c1f10d4346cc7b3c293c894b (patch) | |
tree | 91cf85f0a603b60a9d31721d98785ebf6b7cbb92 | |
parent | 0f86492b09ca82042166a41f6f21b2dbe4f4a464 (diff) | |
download | src-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
-rw-r--r-- | lib/libc/stdio/fread.c | 29 |
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; |