1 files changed, 121 insertions, 0 deletions
diff --git a/libpatch_guess_format.c b/libpatch_guess_format.c
new file mode 100644
index 0000000..48ce419
--- /dev/null
+++ b/libpatch_guess_format.c
@@ -0,0 +1,121 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+
+
+static int
+is_unsigned(const char *text, size_t textlen, size_t *off)
+{
+	if (*off == textlen || !isdigit(text[*off]))
+		return 0;
+	while (isdigit(++*off));
+	return 1;
+}
+
+
+enum libpatch_style
+libpatch_guess_format(const char *text, size_t textlen, size_t *offset)
+{
+	enum libpatch_style guess = LIBPATCH_STYLE_GARBAGE;
+	size_t off = offset ? *offset : 0;
+	size_t two_nums;
+
+	while (off < textlen) {
+		if (text[off] == '+') {
+			if (textlen - off < 3 || strncmp(&text[off], "+++", 3))
+				goto skip_line;
+			goto unified;
+
+		} else if (text[off] == '*') {
+			if (textlen - off < 3 || strncmp(&text[off], "***", 3))
+				goto skip_line;
+			goto copied;
+
+		} else if (text[off] == '@') {
+			if (textlen - off < 3 || strncmp(&text[off], "@@ ", 3))
+				goto skip_line;
+			goto unified;
+
+		} else if (text[off] == 'a') {
+			off++;
+			if (!is_unsigned(text, textlen, &off))
+				goto skip_line;
+			if (off != textlen && text[off] == ' ')
+				off++;
+			if (is_unsigned(text, textlen, &off))
+				goto rcs;
+			else
+				goto ed_alternative;
+
+		} else if (text[off] == 'd') {
+			off++;
+			if (!is_unsigned(text, textlen, &off))
+				goto skip_line;
+			if (off != textlen && text[off] == ' ')
+				off++;
+			if (!is_unsigned(text, textlen, &off))
+				goto ed_alternative;
+			guess = LIBPATCH_STYLE_RCS;
+			/* could also be LIBPATCH_STYLE_ED_ALTERNATIVE,
+			 * whould cannot be parsed so LIBPATCH_STYLE_RCS
+			 * is preferred if the patch happens to be valid
+			 * in both */
+			goto skip_line;
+
+		} else if (text[off] == 'c') {
+			off++;
+			if (!is_unsigned(text, textlen, &off))
+				goto skip_line;
+			goto ed_alternative;
+
+		} else if (isdigit(text[off])) {
+			if (!is_unsigned(text, textlen, &off))
+				goto skip_line;
+			two_nums = (off != textlen && text[off] == ',');
+			if (two_nums) {
+				off += 1;
+				if (!is_unsigned(text, textlen, &off))
+					goto skip_line;
+			}
+			switch (text[off]) {
+			case 'i':
+				goto ed;
+			case 'a':
+				if (two_nums)
+					goto normal;
+				/* fall through */
+			case 'c':
+			case 'd':
+				off++;
+				if (off == textlen || text[off] == '\n')
+					goto ed;
+				else if (isdigit(text[off]))
+					goto normal;
+				/* fall through */
+			default:
+				goto skip_line;
+			}
+
+		} else {
+		skip_line:
+			while (off != textlen && text[off] != '\n')
+				off++;
+			off += (off != textlen);
+		}
+	}
+
+	*offset = off;
+	return guess;
+
+determined:
+	while (off != textlen && text[off] != '\n')
+		off++;
+	*offset = off += (off != textlen);
+	return guess;
+
+normal:         guess = LIBPATCH_STYLE_NORMAL;         goto determined;
+copied:         guess = LIBPATCH_STYLE_COPIED;         goto determined;
+unified:        guess = LIBPATCH_STYLE_UNIFIED;        goto determined;
+ed:             guess = LIBPATCH_STYLE_ED;             goto determined;
+ed_alternative: guess = LIBPATCH_STYLE_ED_ALTERNATIVE; goto determined;
+rcs:            guess = LIBPATCH_STYLE_RCS;            goto determined;
+}