split out utf8 encoding into library

unicode/Makefile

@@ -1,2 +1,12 @@
-utf8: utf8.c
-	$(CC) -I../ascii -g -o utf8 utf8.c
+utf8: utf8.o libunicode.o
+	$(CC) -g -o utf8 libunicode.o utf8.o
+
+libunicode.o:
+
+utf8.o: libunicode.h utf8.c
+	$(CC) -I../ascii -c -g -o utf8.o utf8.c
+
+clean:
+	rm -f *.o utf8
+
+.PHONY: clean

unicode/libunicode.c

@@ -0,0 +1,21 @@
+#include "libunicode.h"
+
+utf8_t utf8(utf32_t c){
+	unsigned char n;
+	utf8_t r;
+
+	r = 0;
+	switch(n = (c < 0x10000) + (c < 0x0800) + (c < 0x0080)){
+	case 0: r = 0xF0 + ((c >> 18) & 0x07); /* 11110xxx */
+	case 1:	r = (r << 8) + (n == 1
+		? 0xE0 + ((c >> 12) & 0x0F) /* 1110xxxx */
+		: 0x50 + ((c >> 12) & 0x3F)); /* 10xxxxxx */
+	case 2:	r = (r << 8) + (n == 2
+		? 0xC0 + ((c >> 6) & 0x1F) /* 110xxxxx */
+		: 0x50 + ((c >> 6) & 0x3F)); /* 10xxxxxx */
+	case 3:	r = (r << 8) + (n == 3
+		? c & 0x7F /* 0xxxxxxx */
+		: 0x50 + (c & 0x3F)); /* 10xxxxxx */
+	}
+	return r;
+}

unicode/libunicode.h

@@ -0,0 +1,14 @@
+#if defined UINT32_MAX /* indicator <stdint.h> is included */
+#	define unicode_codepoint_t uint32_t
+#else
+ /* C99 draft 5.2.4.2.1 Sizes of integer types says unsigned long must be able
+  * to hold 32b */
+#	define unicode_codepoint_t unsigned long
+#endif
+#define utf32_t unicode_codepoint_t
+/* for holding the literal numeric value of a utf8 rune, not for assembling
+ * strings; >=32b value */
+#define utf8_t unicode_codepoint_t
+
+/* encode UTF-32 value into UTF-8 */
+utf8_t utf8(utf32_t c);

unicode/utf8.c

@@ -1,7 +1,8 @@
-#include <stdio.h> /* fprintf(3), getc(3), stderr, stdin, EOF */
-#include <string.h> /* memset(3) */
+#include <stdio.h> /* fprintf(3), getc(3), putc(3) stderr, stdin, EOF */
+#include <string.h> /* strchr(3) */
 #include "ascii.h" /* ASCII_HEXADECIMAL_DIGITS_LOWER,
                     * ASCII_HEXADECIMAL_DIGITS_UPPER */
+#include "libunicode.h" /* utf8(3) */
 #define SKIPLINE while((c = getc(stdin)) != '\n' && c != EOF)
 
 static char *hex = ASCII_HEXADECIMAL_DIGITS_UPPER
@@ -12,16 +13,15 @@ int main(int argc, char *argv[]){
 	int i;
 	int l; /* line counter */
 	char *n;
-	long unsigned int utf32_lit;
-	unsigned char utf8_bytes[8];
+	utf32_t codepoint;
+	utf8_t encoded;
 
 	c = '\0';
 	i = 0;
 	l = 1;
 	while(c != EOF){
-		memset(utf8_bytes, '0', sizeof utf8_bytes);
 		for(
-			i = 0, n = NULL, utf32_lit = 0;
+			i = 0, n = NULL, codepoint = 0;
 			(c = getc(stdin)) != '\n'
 			&& c != EOF
 			&& i < 10;
@@ -41,7 +41,7 @@ int main(int argc, char *argv[]){
 				break;
 			}
 			if(n != NULL)
-				utf32_lit = (utf32_lit << 4) + (n - hex) % 16;
+				codepoint = (codepoint << 4) + (n - hex) % 16;
 		}
 		if(i < 3){
 			if(c != '\n' && c != EOF)
@@ -50,24 +50,10 @@ int main(int argc, char *argv[]){
 				return 0;
 			continue;
 		}
-		/* something with the bit math is broken */
-		switch(i =	(utf32_lit < 0x10000)
-			+ (utf32_lit < 0x0800)
-			+ (utf32_lit < 0x0080)){
-		case 0: utf8_bytes[0] =
-			0xF0 + ((utf32_lit >> 18) & 0x07); /* 11110xxx */
-		case 1:	utf8_bytes[1] = i == 1
-			? 0xE0 + ((utf32_lit >> 12) & 0x0F) /* 1110xxxx */
-			: 0x50 + ((utf32_lit >> 12) & 0x3F); /* 10xxxxxx */
-		case 2:	utf8_bytes[2] = i == 2
-			? 0xC0 + ((utf32_lit >> 6) & 0x1F) /* 110xxxxx */
-			: 0x50 + ((utf32_lit >> 6) & 0x3F); /* 10xxxxxx */
-		case 3:	utf8_bytes[3] = i == 3
-			? utf8_bytes[3] = utf32_lit & 0x7F /* 0xxxxxxx */
-			: 0x50 + (utf32_lit & 0x3F); /* 10xxxxxx */
-		}
-		for( ; i < 4; ++i)
-			putc(utf8_bytes[i], stdout);
+		encoded = utf8(codepoint);
+		for(i = 3; i >= 0; --i)
+			if((encoded >> 8 * i) > 0 || i == 0)
+				putc(encoded >> 8 * i, stdout);
 		++l;
 	}
 }