A simple UTF-8/16/32 encoder/decoder

uchar.c

/* Licensed under the CC0 license */
#include <stdint.h>
#include <string.h>

#define INVALID_CODEPOINT -1
#define UNPAIRED_SURROGATE -2

int utf32_to_utf8(uint32_t ch, uint8_t **out)
{
	int len = 0;
	char obytes[5];

	if (ch >= 0xD800 && ch <= 0xDFFF)
		return UNPAIRED_SURROGATE;

	if (ch <= 0x7F) {
		len = 2;
		obytes[0] = (uint8_t)ch;
		obytes[1] = 0;
	} else if (ch <= 0x7FF) {
		len = 3;
		obytes[0] = ((ch >> 6) & 037) | 0300;
		obytes[1] = ((ch & 077) | 0200);
		obytes[2] = 0;
	} else if (ch <= 0xFFFF) {
		len = 4;
		obytes[0] = ((ch >> 12) & 017) | 0340;
		obytes[1] = ((ch >> 6) & 077) | 0200;
		obytes[2] = ((ch & 077) | 0200);
		obytes[3] = 0;
	} else if (ch <= 0x10FFFF) {
		len = 5;
		obytes[0] = ((ch >> 18) & 070) | 0360;
		obytes[1] = ((ch >> 12) & 077) | 0200;
		obytes[2] = ((ch >> 6) & 077) | 0200;
		obytes[3] = ((ch & 077) | 0200);
		obytes[4] = 0;
	} else
		return INVALID_CODEPOINT;

	*out = (uint8_t *)malloc(sizeof(uint8_t) * len);
	memcpy(*out, obytes, len);
	return len;
}

int utf8_to_utf32(uint8_t *in)
{
	int ch = 0;
	if (in[0] <= 0x7F) {
		ch = in[0];
	} else if (ch <= 0xD0) {
		ch |= (in[0] & 037) << 6;
		ch |= (in[1] & 077);
	} else if (ch <= 0xE0) {
		ch |= (in[0] & 017) << 12;
		ch |= (in[1] & 077) << 6;
		ch |= (in[2] & 077);
	} else if (ch <= 0xF7) {
		ch |= (in[0] & 007) << 18;
		ch |= (in[1] & 077) << 12;
		ch |= (in[2] & 077) << 6;
		ch |= (in[3] & 077);
	} else
		return INVALID_CODEPOINT;

	if (ch >= 0xD800 && ch <= 0xDFFF)
		return UNPAIRED_SURROGATE;
	return ch;
}

int utf32_to_utf16(uint32_t ch, uint16_t **out)
{
	if (ch >= 0xD800 && ch <= 0xDFFF)
		return UNPAIRED_SURROGATE;
	int len;
	uint16_t ounits[3];

	if (ch <= 0xFFFF) {
		ounits[0] = (uint16_t)ch;
		ounits[1] = 0;
		len = 2;
	} else if (ch <= 0x10FFFF) {
		ch &= 0xFFFF;
		ounits[0] = (ch >> 10) | 0xD800;
		ounits[1] = (ch & 0x3FF) | 0xDC00;
		ounits[2] = 0;
		len = 3;
	} else
		return INVALID_CODEPOINT;

	*out = (uint16_t *)(malloc(sizeof(uint16_t) * len));
	memcpy(*out, ounits, sizeof(uint16_t) * len);

	return len;
}

int utf16_to_utf32(uint16_t *in)
{
	int ch = 0;
	if (in[0] < 0xD800 || in[0] > 0xDFFF) {
		ch = in[0];
	} else {
		ch |= (in[0] & 0x3FF) << 10;
		ch |= in[1] & 0x3FF;
		ch |= 0x10000;
	}
	
	if (ch > 0x10FFFF)
		return INVALID_CODEPOINT;
	
	if (ch >= 0xD800 && ch <= 0xDFFF)
		return UNPAIRED_SURROGATE;
	return ch;
}

int utf16_to_utf8(uint16_t *in, uint8_t **out)
{
	return utf32_to_utf8(utf16_to_utf32(in), out);
}

int utf8_to_utf16(uint8_t *in, uint16_t **out)
{
	return utf32_to_utf16(utf8_to_utf32(in), out);
}