utf32 -> utf8

// Ref: http://clang.llvm.org/doxygen/ConvertUTF_8c_source.html
#import <Foundation/Foundation.h>

static uint8_t const firstByteMark[7] = { 0x00, 0x00, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC };
static uint32_t const byteMark = 0x80; 
static uint32_t const byteMask = 0xBF;

int main(int argc, char *argv[]) {
	unsigned int input = strtol("0001F30D", NULL, 16);
	
	size_t const len = input < 0x80    ? 1
	                 : input < 0x800   ? 2
	                 : input < 0x10000 ? 3
	                                   : 4;
	
	uint8_t bytes[len];
	uint8_t *str = bytes+len;
	switch(len) {
	    case 4: *--str = (uint8_t)((input | byteMark) & byteMask); input >>= 6;
	    case 3: *--str = (uint8_t)((input | byteMark) & byteMask); input >>= 6;
	    case 2: *--str = (uint8_t)((input | byteMark) & byteMask); input >>= 6;
	    case 1: *--str = (uint8_t) (input | firstByteMark[len]);
	}
	
	NSLog(@"'%@'", [[NSString alloc] initWithBytes:(char*)str length:len encoding:NSUTF8StringEncoding]);
}