1 files changed, 106 insertions, 0 deletions
diff --git a/lib/libc/stdio/fwrite_unlocked.c b/lib/libc/stdio/fwrite_unlocked.c
new file mode 100644
index 00000000..dd5f4c0b
--- /dev/null
+++ b/lib/libc/stdio/fwrite_unlocked.c
@@ -0,0 +1,106 @@
+#include "__stdio.h"
+#include <atomic.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+extern void __libc_init_io(void);
+void *__libc_force_io_init = (void *)__libc_init_io;
+
+size_t fwrite_unlocked(const void *restrict ptr, size_t size, size_t nitems, FILE *restrict stream)
+{
+	size_t total_bytes;
+	size_t written = 0;
+	const char *data = (const char *)ptr;
+
+	if (ptr == NULL || stream == NULL || size == 0) {
+		if (size == 0) {
+			return nitems;
+		}
+		errno = EINVAL;
+		return 0;
+	}
+
+	if (__builtin_mul_overflow(size, nitems, &total_bytes)) {
+		errno = EOVERFLOW;
+		return 0;
+	}
+
+	if ((stream->flags & O_ACCMODE) == O_RDONLY) {
+		errno = EBADF;
+		return 0;
+	}
+
+	if (stream->flags & _IO_ERR) {
+		errno = EIO;
+		return 0;
+	}
+
+	/* Handle in-memory buffer case (e.g., string streams) */
+	if (stream->fd == -1 && stream->buf != NULL) {
+		size_t space_left = (stream->buf_size > stream->buf_len) ?
+					    stream->buf_size - stream->buf_len - 1 /* Reserve for '\0' */
+					    :
+					    0;
+		if (space_left == 0) {
+			return 0;
+		}
+		size_t to_copy = (total_bytes < space_left) ? total_bytes : space_left;
+		if (to_copy > 0) {
+			memcpy(stream->buf + stream->buf_len, data, to_copy);
+			stream->buf_len += to_copy;
+		}
+		return (to_copy == total_bytes) ? nitems : to_copy / size;
+	}
+
+	if (stream->type != _IONBF && stream->buf == NULL) {
+		errno = EIO;
+		return 0;
+	}
+
+	/* Unbuffered mode: direct write */
+	if (stream->type == _IONBF) {
+		ssize_t result = write(stream->fd, data, total_bytes);
+		if (result < 0) {
+			stream->flags |= _IO_ERR;
+			return 0;
+		}
+		return (result == (ssize_t)total_bytes) ? nitems : result / size;
+	}
+
+	size_t remaining = total_bytes;
+	while (remaining > 0) {
+		size_t space_available = stream->buf_size - stream->buf_len;
+		if (space_available == 0) {
+			if (fflush_unlocked(stream) != 0) {
+				return written / size;
+			}
+			space_available = stream->buf_size;
+		}
+		size_t to_copy = (remaining < space_available) ? remaining : space_available;
+		memcpy(stream->buf + stream->buf_len, data + written, to_copy);
+		stream->buf_len += to_copy;
+		written += to_copy;
+		remaining -= to_copy;
+
+		/* Line-buffered: flush on newline in the copied chunk */
+		if (stream->type == _IOLBF) {
+			char *newline_pos = memchr(stream->buf + stream->buf_len - to_copy, '\n', to_copy);
+			if (newline_pos != NULL) {
+				if (fflush_unlocked(stream) != 0) {
+					return written / size;
+				}
+			}
+		} else if (stream->type == _IOFBF && stream->buf_len == stream->buf_size) {
+			/* Full-buffered: flush when buffer is full */
+			if (fflush_unlocked(stream) != 0) {
+				return written / size;
+			}
+		}
+	}
+
+	return (written == total_bytes) ? nitems : written / size;
+}