Add u8lower()

2 files changed, 48 insertions, 0 deletions

diff --git a/include/unicode/string.h b/include/unicode/string.h
index 6197235..0c1786c 100644
--- a/include/unicode/string.h
+++ b/include/unicode/string.h
@@ -16,6 +16,8 @@ enum [[clang::__flag_enum__]] caseflags {
 size_t u8glen(const char8_t *, size_t);
 size_t u8gnext(struct u8view *, const char8_t **, size_t *);
 
+size_t u8lower(char8_t *restrict, size_t, const char8_t *, size_t,
+               enum caseflags);
 size_t u8upper(char8_t *restrict, size_t, const char8_t *, size_t,
                enum caseflags);
 
diff --git a/lib/unicode/string/u8lower.c b/lib/unicode/string/u8lower.c
new file mode 100644
index 0000000..052217f
--- /dev/null
+++ b/lib/unicode/string/u8lower.c
@@ -0,0 +1,46 @@
+#include "mbstring.h"
+#include "unicode/prop.h"
+#include "unicode/string.h"
+
+constexpr rune COMB_GRAVE     = 0x0300;
+constexpr rune COMB_ACUTE     = 0x0301;
+constexpr rune COMB_TILDE     = 0x0303;
+constexpr rune COMB_DOT_ABOVE = 0x0307;
+
+size_t
+u8lower(char8_t *restrict dst, size_t dstn, const char8_t *src, size_t srcn,
+        enum caseflags flags)
+{
+	struct lcctx ctx = {
+		.az_or_tr = flags & CF_LANG_AZ,
+		.lt = flags & CF_LANG_LT,
+	};
+
+	rune ch;
+	size_t n = 0;
+
+	while (u8next(&ch, &src, &srcn)) {
+		/* TODO: Set ‘eow’ once word-segmentation is implemented */
+
+		rune next = 0;
+		if (srcn > 0)
+			u8tor(&next, src);
+		ctx.before_dot = next == COMB_DOT_ABOVE;
+		ctx.before_acc = next == COMB_GRAVE
+		              || next == COMB_ACUTE
+		              || next == COMB_TILDE;
+
+		struct rview rv = uprop_get_lc(ch, ctx);
+		for (size_t i = 0; i < rv.len; i++) {
+			if (n >= dstn) {
+				char8_t buf[U8_LEN_MAX];
+				n += rtou8(buf, sizeof(buf), rv.p[i]);
+			} else
+				n += rtou8(dst + n, dstn - n, rv.p[i]);
+		}
+
+		ctx.after_I = ch == 'I';
+	}
+
+	return n;
+}