From 5ecd0fc61a1a292426538fcb1e791342e04953b5 Mon Sep 17 00:00:00 2001
From: Thomas Voss <thomas.voss@humanwave.nl>
Date: Wed, 6 Mar 2024 16:41:59 +0100
Subject: Genesis

---
 lib/mbstring/u8rchr.c | 87 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 lib/mbstring/u8rchr.c

(limited to 'lib/mbstring/u8rchr.c')

diff --git a/lib/mbstring/u8rchr.c b/lib/mbstring/u8rchr.c
new file mode 100644
index 0000000..b92c323
--- /dev/null
+++ b/lib/mbstring/u8rchr.c
@@ -0,0 +1,87 @@
+#include <stddef.h>
+#include <stdint.h>
+
+#define _RUNE_NO_MACRO_WRAPPER 1
+#include "mbstring.h"
+
+static char8_t *
+memrchr1(const char8_t *s, size_t k, const char8_t *n)
+{
+	for (const char8_t *p = s + k - 1; k-- > 0; p--) {
+		if (*p == *n)
+			return (char8_t *)p;
+	}
+	return nullptr;
+}
+
+static char8_t *
+memrchr2(const char8_t *h, size_t k, const char8_t *n)
+{
+	uint16_t hw, nw;
+	const char8_t *H = h + k - 1;
+	hw = H[-1] << 8 | H[-0];
+	nw = n[+0] << 8 | n[+1];
+
+	for (H -= 2, k -= 2; k; k--, hw = hw >> 8 | (*H-- << 8)) {
+		if (hw == nw)
+			return (char8_t *)H + 1;
+	}
+
+	return hw == nw ? (char8_t *)H + 1 : nullptr;
+}
+
+static char8_t *
+memrchr3(const char8_t *h, size_t k, const char8_t *n)
+{
+	uint32_t hw, nw;
+	const char8_t *H = h + k - 1;
+	hw = H[-2] << 24 | H[-1] << 16 | H[-0] << 8;
+	nw = n[+0] << 24 | n[+1] << 16 | n[+2] << 8;
+
+	for (H -= 3, k -= 3; k;
+	     k--, hw = (hw >> 8 | (*H-- << 24)) & UINT32_C(0xFFFFFF00))
+	{
+		if (hw == nw)
+			return (char8_t *)H + 1;
+	}
+
+	return hw == nw ? (char8_t *)H + 1 : nullptr;
+}
+
+static char8_t *
+memrchr4(const char8_t *h, size_t k, const char8_t *n)
+{
+	uint32_t hw, nw;
+	const char8_t *H = h + k - 1;
+	hw = H[-3] << 24 | H[-2] << 16 | H[-1] << 8 | H[-0];
+	nw = n[+0] << 24 | n[+1] << 16 | n[+2] << 8 | n[+3];
+
+	for (H -= 4, k -= 4; k; k--, hw = hw >> 8 | (*H-- << 24)) {
+		if (hw == nw)
+			return (char8_t *)H + 1;
+	}
+
+	return hw == nw ? (char8_t *)H + 1 : nullptr;
+}
+
+char8_t *
+u8rchr(const char8_t *s, rune ch, size_t n)
+{
+	char8_t buf[U8_LEN_MAX];
+	int m = rtou8(buf, ch, sizeof(buf));
+
+	if (n < (size_t)m)
+		return nullptr;
+	switch (m) {
+	case 1:
+		return (char8_t *)memrchr1(s, n, buf);
+	case 2:
+		return (char8_t *)memrchr2(s, n, buf);
+	case 3:
+		return (char8_t *)memrchr3(s, n, buf);
+	case 4:
+		return (char8_t *)memrchr4(s, n, buf);
+	}
+
+	unreachable();
+}
-- 
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