From e4e8b674cc75b545bb30045f73484c6011efe1de Mon Sep 17 00:00:00 2001
From: Mattias Andrée <m@maandree.se>
Date: Mon, 26 Jan 2026 20:35:11 +0100
Subject: Add stacked
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Signed-off-by: Mattias Andrée <m@maandree.se>
---
 Makefile              |  6 +++--
 convert-to-stacked.c  |  4 ++++
 libcharconv.h         |  5 ++++
 libcharconv_latin.c   |  4 ++++
 libcharconv_stacked.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 83 insertions(+), 2 deletions(-)
 create mode 100644 convert-to-stacked.c
 create mode 100644 libcharconv_stacked.c

diff --git a/Makefile b/Makefile
index c26efd0..daa284e 100644
--- a/Makefile
+++ b/Makefile
@@ -84,7 +84,8 @@ BIN =\
 	convert-to-enclosed\
 	convert-to-metrical\
 	convert-to-dentistry\
-	convert-to-cards
+	convert-to-cards\
+	convert-to-stacked
 
 LIBOBJ =\
 	libcharconv_decode_utf8_.o\
@@ -161,7 +162,8 @@ LIBOBJ =\
 	libcharconv_enclosed_negative.o\
 	libcharconv_metrical.o\
 	libcharconv_dentistry.o\
-	libcharconv_cards.o
+	libcharconv_cards.o\
+	libcharconv_stacked.o
 
 LOBJ = $(LIBOBJ:.o=.lo)
 
diff --git a/convert-to-stacked.c b/convert-to-stacked.c
new file mode 100644
index 0000000..119655f
--- /dev/null
+++ b/convert-to-stacked.c
@@ -0,0 +1,4 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+
+SIMPLE(libcharconv_stacked)
diff --git a/libcharconv.h b/libcharconv.h
index 8e5e1a6..5d93d41 100644
--- a/libcharconv.h
+++ b/libcharconv.h
@@ -496,6 +496,11 @@ LIBCHARCONV_FUNC_(libcharconv_dentistry);
  */
 LIBCHARCONV_FUNC_(libcharconv_cards);
 
+/**
+ * Stack characters vertically
+ */
+LIBCHARCONV_FUNC_(libcharconv_stacked);
+
 
 #undef LIBCHARCONV_FUNC_
 #endif
diff --git a/libcharconv_latin.c b/libcharconv_latin.c
index 473896a..f441d0c 100644
--- a/libcharconv_latin.c
+++ b/libcharconv_latin.c
@@ -1070,6 +1070,10 @@ libcharconv_latin(const char *s, size_t slen, size_t *n, uint_least32_t *cp, siz
 			case UINT32_C(0x2666): c1 = 'D'; goto conv1;
 			case UINT32_C(0x2667): c1 = 'c'; goto conv1;
 
+			/* stacked */
+			case UINT32_C(0x2051): c1 = '*'; c2 = '*'; goto conv2;
+			case UINT32_C(0x2E49): c1 = ','; c2 = ','; goto conv2;
+
 			default:
 			no_match:
 				*n += clen;
diff --git a/libcharconv_stacked.c b/libcharconv_stacked.c
new file mode 100644
index 0000000..6f89834
--- /dev/null
+++ b/libcharconv_stacked.c
@@ -0,0 +1,66 @@
+/* See LICENSE file for copyright and license details. */
+#include "lib-common.h"
+
+
+static struct {
+	uint_least32_t a;
+	uint_least32_t b;
+	uint_least32_t to;
+} pairs[] = {
+	{(uint_least32_t)'*', (uint_least32_t)'*', UINT32_C(0x2051)},
+	{(uint_least32_t)',', (uint_least32_t)',', UINT32_C(0x2E49)}
+};
+
+
+enum libcharconv_result
+libcharconv_stacked(const char *s, size_t slen, size_t *n, uint_least32_t *cp, size_t *ncp)
+{
+	uint_least32_t a, b;
+	size_t i, alen, blen;
+	*n = 0;
+	while (slen) {
+		alen = libcharconv_decode_utf8_(s, slen, &a);
+		if (alen > slen) {
+			if (*n)
+				goto no_conv;
+			return LIBCHARCONV_INDETERMINATE;
+		}
+		if (!alen) {
+			*n += 1u;
+			slen -= 1u;
+			s = &s[1];
+			continue;
+		}
+
+		for (i = 0u; i < sizeof(pairs) / sizeof(*pairs); i++) {
+			if (a != pairs[i].a)
+				continue;
+			if (*n)
+				goto no_conv;
+			if (slen == alen)
+				return LIBCHARCONV_INDETERMINATE;
+			blen = libcharconv_decode_utf8_(&s[alen], slen - alen, &b);
+			if (blen > slen)
+				return LIBCHARCONV_INDETERMINATE;
+			if (!blen)
+				goto no_conv;
+			if (b == pairs[i].b)
+				goto conv;
+		}
+
+		*n += alen;
+		s = &s[alen];
+		slen -= alen;
+	}
+no_conv:
+	return LIBCHARCONV_NO_CONVERT;
+
+conv:
+	if (*n)
+		goto no_conv;
+	if (*ncp)
+		*cp = pairs[i].to;
+	*n += alen + blen;
+	*ncp = 1u;
+	return LIBCHARCONV_CONVERTED;
+}
-- 
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