1 files changed, 38 insertions, 0 deletions
diff --git a/src/stdio/__underflow.c b/src/stdio/__underflow.c
new file mode 100644
index 00000000..b769f4e4
--- /dev/null
+++ b/src/stdio/__underflow.c
@@ -0,0 +1,38 @@
+#include "stdio_impl.h"
+
+int __underflow(FILE *f)
+{
+	ssize_t cnt;
+
+	/* Read from buffer (Do we ever get called when this is true??) */
+	if (f->rpos < f->rstop) return *f->rpos;
+
+	/* Initialize if we're not already reading */
+	if (!f->rstop) {
+		/* Fail immediately if unreadable, eof, or error state. */
+		if (f->flags & (F_EOF|F_ERR|F_NORD)) return EOF;
+
+		/* Set byte orientation -1,0=>-1; 1=>1 */
+		f->mode |= f->mode-1;
+
+		/* Flush any unwritten output; fail on error. */
+		if (f->wpos > f->buf && __oflow(f)) return EOF;
+
+		/* Disallow writes to buffer. */
+		f->wstop = 0;
+	}
+
+	/* Perform the underlying read operation */
+	if ((cnt=f->read(f, f->buf, f->buf_size)) + 1 <= 1) {
+		/* Set flags and leave read mode */
+		f->flags |= F_EOF | (cnt & F_ERR);
+		f->rpos = f->rend = f->rstop = 0;
+		return EOF;
+	}
+
+	/* Setup buffer pointers for reading from buffer */
+	f->rpos = f->buf;
+	f->rend = f->rstop = f->buf + cnt;
+
+	return *f->rpos;
+}