[*] Initial commit

lonetix/utf/utfrrune.c

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+// SPDX-License-Identifier: LGPL-3.0-or-later
+
+/**
+ * \file utf/utfrrune.c
+ *
+ * Implements `utfrrune()`.
+ *
+ * \copyright The DoubleFourteen Code Forge (C) All Rights Reserved
+ * \author    Lorenzo Cogotti
+ */
+
+/*
+ * This work is derived from Plan 9 libutf, see utf/utf.h for details.
+ * Original license terms follow:
+ *
+ * The authors of this software are Rob Pike and Ken Thompson.
+ *              Copyright (c) 2002 by Lucent Technologies.
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose without fee is hereby granted, provided that this entire notice
+ * is included in all copies of any software which is or includes a copy
+ * or modification of this software and in all copies of the supporting
+ * documentation for such software.
+ * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
+ * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHORS NOR LUCENT TECHNOLOGIES MAKE
+ * ANY REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
+ * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
+ *
+ * The original libutf library is available at: https://9fans.github.io/plan9port/unix/libutf.tgz
+ */
+
+#include "utf/utf.h"
+
+#include <string.h>
+
+char *utfrrune(const char *s, Rune c)
+{
+	if (c < RUNE_SYNC)
+		return strrchr(s, c);
+
+	char *s1 = NULL;
+	while (TRUE) {
+		Rune c1 = *(const Uint8 *) s;
+		if (c1 < RUNE_SELF) {  // one byte rune
+			if (c1 == '\0')
+				break;
+
+			if (RUNE_SYNC != RUNE_SELF && c1 == c)  // exposition only, optimized away, see topmost if ()
+				s1 = (char *) s;
+
+			s++;
+			continue;
+		}
+
+		Rune   r;
+		size_t n = chartorune(&r, s);
+		if (r == c)
+			s1 = (char *) s;
+
+		s += n;
+	}
+	return s1;
+}