Optimized fread.
This makes us competitive with glibc for fully-buffered and unbuffered reads,
except in single-threaded situations where glibc avoids locking, but since
we're never really single-threaded anyway, that isn't a priority.
Bug: 18593728
Change-Id: Ib776bfba422ccf46209581fc0dc54f3567645b8f
diff --git a/libc/stdio/fread.c b/libc/stdio/fread.c
index e052128..9e5758f 100644
--- a/libc/stdio/fread.c
+++ b/libc/stdio/fread.c
@@ -35,6 +35,7 @@
#include <string.h>
#include <stdint.h>
#include <errno.h>
+#include <sys/param.h>
#include "local.h"
#define MUL_NO_OVERFLOW (1UL << (sizeof(size_t) * 4))
@@ -42,13 +43,8 @@
size_t
fread(void *buf, size_t size, size_t count, FILE *fp)
{
- size_t resid;
- char *p;
- int r;
- size_t total;
-
/*
- * Extension: Catch integer overflow
+ * Extension: Catch integer overflow.
*/
if ((size >= MUL_NO_OVERFLOW || count >= MUL_NO_OVERFLOW) &&
size > 0 && SIZE_MAX / size < count) {
@@ -57,48 +53,81 @@
return (0);
}
+ const size_t desired_total = count * size;
+ size_t total = desired_total;
+
/*
* ANSI and SUSv2 require a return value of 0 if size or count are 0.
*/
- if ((resid = count * size) == 0)
+ if (total == 0) {
return (0);
+ }
+
FLOCKFILE(fp);
_SET_ORIENTATION(fp, -1);
+
+ // TODO: how can this ever happen?!
if (fp->_r < 0)
fp->_r = 0;
- total = resid;
- p = buf;
- // BEGIN android-added
- // Avoid pathological behavior on unbuffered files. OpenBSD
- // will loop reading one byte then memcpying one byte!
- if ((fp->_flags & __SNBF) != 0) {
- // We know if we're unbuffered that our buffer is empty, so
- // we can just read directly.
- while (resid > 0 && (r = (*fp->_read)(fp->_cookie, p, resid)) > 0) {
- p += r;
- resid -= r;
- }
- FUNLOCKFILE(fp);
- return ((total - resid) / size);
+ /*
+ * Ensure _bf._size is valid.
+ */
+ if (fp->_bf._base == NULL) {
+ __smakebuf(fp);
}
- // END android-added
- while (resid > (size_t)(r = fp->_r)) {
- (void)memcpy((void *)p, (void *)fp->_p, (size_t)r);
- fp->_p += r;
- /* fp->_r = 0 ... done in __srefill */
- p += r;
- resid -= r;
+ char* dst = buf;
+
+ while (total > 0) {
+ /*
+ * Copy data out of the buffer.
+ */
+ size_t buffered_bytes = MIN(fp->_r, total);
+ memcpy(dst, fp->_p, buffered_bytes);
+ fp->_p += buffered_bytes;
+ fp->_r -= buffered_bytes;
+ dst += buffered_bytes;
+ total -= buffered_bytes;
+
+ /*
+ * Are we done?
+ */
+ if (total == 0) {
+ goto out;
+ }
+
+ /*
+ * Do we have so much more to read that we should
+ * avoid copying it through the buffer?
+ */
+ if (total > (size_t) fp->_bf._size) {
+ break;
+ }
+
+ /*
+ * Less than a buffer to go, so refill the buffer and
+ * go around the loop again.
+ */
if (__srefill(fp)) {
- /* no more input: return partial result */
- FUNLOCKFILE(fp);
- return ((total - resid) / size);
+ goto out;
}
}
- (void)memcpy((void *)p, (void *)fp->_p, resid);
- fp->_r -= resid;
- fp->_p += resid;
+
+ /*
+ * Read directly into the caller's buffer.
+ */
+ while (total > 0) {
+ ssize_t bytes_read = (*fp->_read)(fp->_cookie, dst, total);
+ if (bytes_read <= 0) {
+ fp->_flags = (fp->_r == 0) ? __SEOF : __SERR;
+ break;
+ }
+ dst += bytes_read;
+ total -= bytes_read;
+ }
+
+out:
FUNLOCKFILE(fp);
- return (count);
+ return ((desired_total - total) / size);
}
diff --git a/tests/stdio_test.cpp b/tests/stdio_test.cpp
index de5eea3..6d7e72b 100644
--- a/tests/stdio_test.cpp
+++ b/tests/stdio_test.cpp
@@ -888,3 +888,25 @@
ASSERT_EQ('\xff', buf[i]);
}
}
+
+TEST(fread, fread_EOF) {
+ const char* digits = "0123456789";
+ FILE* fp = fmemopen((char*) digits, sizeof(digits), "r");
+
+ // Try to read too much, but little enough that it still fits in the FILE's internal buffer.
+ char buf1[4 * 4];
+ memset(buf1, 0, sizeof(buf1));
+ ASSERT_EQ(2U, fread(buf1, 4, 4, fp));
+ ASSERT_STREQ(buf1, "01234567");
+ ASSERT_TRUE(feof(fp));
+
+ rewind(fp);
+
+ char buf2[4 * 4];
+ memset(buf2, 0, sizeof(buf2));
+ ASSERT_EQ(2U, fread(buf2, 4, 4096, fp));
+ ASSERT_STREQ(buf2, "01234567");
+ ASSERT_TRUE(feof(fp));
+
+ fclose(fp);
+}