From 9efad5f8d3ebbecdf8221d871f43bcbd15f1ac7d Mon Sep 17 00:00:00 2001
From: Anton Kling <anton@kling.gg>
Date: Sun, 22 Oct 2023 23:22:32 +0200
Subject: libc: Add a cache to the fread function for reading from files on
disk.
This helps a ton when using functions such as fscanf that reads from a
FILE byte by byte. By creating a cache it avoids a ton of 'read'
syscalls that would otherwise be made.
---
userland/libc/stdio/stdin.c | 33 +++++++++++++++++++++++++++++++--
1 file changed, 31 insertions(+), 2 deletions(-)
(limited to 'userland/libc/stdio/stdin.c')
diff --git a/userland/libc/stdio/stdin.c b/userland/libc/stdio/stdin.c
index ae3ab8d..2e1e50f 100644
--- a/userland/libc/stdio/stdin.c
+++ b/userland/libc/stdio/stdin.c
@@ -12,7 +12,7 @@ size_t write_fd(FILE *f, const unsigned char *s, size_t l) {
return rc;
}
-size_t read_fd(FILE *f, unsigned char *s, size_t l) {
+size_t non_cache_read_fd(FILE *f, unsigned char *s, size_t l) {
int rc = pread(f->fd, s, l, f->offset_in_file);
if (rc == 0)
f->is_eof = 1;
@@ -20,11 +20,40 @@ size_t read_fd(FILE *f, unsigned char *s, size_t l) {
f->has_error = 1;
return 0;
}
- f->offset_in_file += rc;
return rc;
}
+size_t read_fd(FILE *f, unsigned char *s, size_t l) {
+ if (0 == l)
+ return 0;
+ if (!f->read_buffer) {
+ f->read_buffer = malloc(4096);
+ f->read_buffer_stored = 0;
+ f->read_buffer_has_read = 0;
+ }
+ if (f->read_buffer_stored > 0) {
+ size_t read_len = min(l, f->read_buffer_stored);
+ f->offset_in_file += read_len;
+ memcpy(s, f->read_buffer + f->read_buffer_has_read, read_len);
+ f->read_buffer_stored -= read_len;
+ f->read_buffer_has_read += read_len;
+ s += read_len;
+ l -= read_len;
+ return read_len + read_fd(f, s, l);
+ }
+ if (0 == f->read_buffer_stored) {
+ f->read_buffer_stored = non_cache_read_fd(f, f->read_buffer, 4096);
+ f->read_buffer_has_read = 0;
+ if (0 == f->read_buffer_stored) {
+ return 0;
+ }
+ return read_fd(f, s, l);
+ }
+ assert(0);
+}
+
int seek_fd(FILE *stream, long offset, int whence) {
+ stream->read_buffer_stored = 0;
switch (whence) {
case SEEK_SET:
stream->offset_in_file = offset;
--
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