1 files changed, 68 insertions, 0 deletions
diff --git a/libc/stdio/_adjust_pos.c b/libc/stdio/_adjust_pos.c
new file mode 100644
index 000000000..bc48d32b7
--- /dev/null
+++ b/libc/stdio/_adjust_pos.c
@@ -0,0 +1,68 @@
+/* Copyright (C) 2004       Manuel Novoa III    <mjn3@codepoet.org>
+ *
+ * GNU Library General Public License (LGPL) version 2 or later.
+ *
+ * Dedicated to Toni.  See uClibc/DEDICATION.mjn3 for details.
+ */
+
+#include "_stdio.h"
+
+/* Both ftell() and fseek() (for SEEK_CUR) need to correct the stream's
+ * position to take into account buffered data and ungotten chars.
+ *
+ * If successful, store corrected position in *pos and return >= 0.
+ * Otherwise return < 0.
+ *
+ * If position is unrepresentable, set errno to EOVERFLOW.
+ */
+
+int __stdio_adjust_position(register FILE * __restrict stream,
+							register __offmax_t *pos)
+{
+	__offmax_t oldpos;
+	int corr;
+
+	if ((corr = stream->__modeflags & __MASK_READING) != 0) {
+		--corr;	/* Correct for ungots. Assume narrow, and fix below. */
+	}
+
+#ifdef __UCLIBC_HAS_WCHAR__
+	if (corr && __STDIO_STREAM_IS_WIDE(stream)) {
+		/* A wide stream and we have at least one ungotten wchar.
+		 * If it is a user ungot, we need to fail since position
+		 * is unspecified as per C99. */
+		if ((corr > 1) || stream->__ungot[1]) { /* User ungetwc, */
+			return -1;			/* so position is undefined. */
+		}
+		corr -= (1 + stream->__ungot_width[1]);
+		if (stream->__state.__mask > 0) { /* Incomplete (bad?) mb char. */
+			corr -= stream->__ungot_width[0];
+		}
+	}
+#endif
+
+#ifdef __STDIO_BUFFERS
+	corr += (((__STDIO_STREAM_IS_WRITING(stream))
+			  ? stream->__bufstart : stream->__bufread)
+			 - stream->__bufpos);
+#endif
+
+	oldpos = *pos;
+
+	/* Range checking cases:
+	 * (pos - corr >  pos) && (corr >  0) : underflow?  return -corr < 0
+	 * (pos - corr >  pos) && (corr <  0) : ok .. return -corr > 0
+	 * (pos - corr <= pos) && (corr >= 0) : ok .. return  corr > 0
+	 * (pos - corr <= pos) && (corr <  0) : overflow ..  return corr < 0
+	 */
+
+	if ((*pos -= corr) > oldpos) {
+		corr = -corr;
+	}
+
+	if (corr < 0) {
+		__set_errno(EOVERFLOW);
+	}
+
+	return corr;
+}