1 files changed, 46 insertions, 0 deletions
diff --git a/quantum/unicode/utf8.c b/quantum/unicode/utf8.c
new file mode 100644
index 0000000000..4b2cd4d8d4
--- /dev/null
+++ b/quantum/unicode/utf8.c
@@ -0,0 +1,46 @@
+/* Copyright 2021 QMK
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "utf8.h"
+
+// Borrowed from https://nullprogram.com/blog/2017/10/06/
+const char *decode_utf8(const char *str, int32_t *code_point) {
+    const char *next;
+
+    if (str[0] < 0x80) { // U+0000-007F
+        *code_point = str[0];
+        next        = str + 1;
+    } else if ((str[0] & 0xE0) == 0xC0) { // U+0080-07FF
+        *code_point = ((int32_t)(str[0] & 0x1F) << 6) | ((int32_t)(str[1] & 0x3F) << 0);
+        next        = str + 2;
+    } else if ((str[0] & 0xF0) == 0xE0) { // U+0800-FFFF
+        *code_point = ((int32_t)(str[0] & 0x0F) << 12) | ((int32_t)(str[1] & 0x3F) << 6) | ((int32_t)(str[2] & 0x3F) << 0);
+        next        = str + 3;
+    } else if ((str[0] & 0xF8) == 0xF0 && (str[0] <= 0xF4)) { // U+10000-10FFFF
+        *code_point = ((int32_t)(str[0] & 0x07) << 18) | ((int32_t)(str[1] & 0x3F) << 12) | ((int32_t)(str[2] & 0x3F) << 6) | ((int32_t)(str[3] & 0x3F) << 0);
+        next        = str + 4;
+    } else {
+        *code_point = -1;
+        next        = str + 1;
+    }
+
+    // part of a UTF-16 surrogate pair - invalid
+    if (*code_point >= 0xD800 && *code_point <= 0xDFFF) {
+        *code_point = -1;
+    }
+
+    return next;
+}