src/wctomb.c

/*
#include	<sys/types.h>
#include	<stdio.h>
#include	<stdlib.h>
#include	<string.h>
#include	<unistd.h>
#include	<errno.h>
*/

/*
	the our_* routines are implementations for the corresponding library
	routines. for a while, i tried to actually name them wctomb etc
	but stopped that after i found a system which made wchar_t an
	unsigned char.
*/
enum
{
	T1	= 0x00,
	Tx	= 0x80,
	T2	= 0xC0,
	T3	= 0xE0,
	T4	= 0xF0,
	T5	= 0xF8,
	T6	= 0xFC,

	Bit1	= 7,
	Bitx	= 6,
	Bit2	= 5,
	Bit3	= 4,
	Bit4	= 3,
	Bit5	= 2,
	Bit6	= 2,

	Mask1	= (1<<Bit1)-1,
	Maskx	= (1<<Bitx)-1,
	Mask2	= (1<<Bit2)-1,
	Mask3	= (1<<Bit3)-1,
	Mask4	= (1<<Bit4)-1,
	Mask5	= (1<<Bit5)-1,
	Mask6	= (1<<Bit6)-1,

	Wchar1	= (1UL<<Bit1)-1,
	Wchar2	= (1UL<<(Bit2+Bitx))-1,
	Wchar3	= (1UL<<(Bit3+2*Bitx))-1,
	Wchar4	= (1UL<<(Bit4+3*Bitx))-1,
	Wchar5	= (1UL<<(Bit5+4*Bitx))-1

#ifndef	EILSEQ
	, /* we hate ansi c's comma rules */
	EILSEQ	= 123
#endif /* PLAN9 */
};

static int
our_wctomb(char *s, unsigned long wc)
{
	if(s == 0)
		return 0;		/* no shift states */
	if(wc & ~Wchar2) {
		if(wc & ~Wchar4) {
			if(wc & ~Wchar5) {
				/* 6 bytes */
				s[0] = T6 | ((wc >> 5*Bitx) & Mask6);
				s[1] = Tx | ((wc >> 4*Bitx) & Maskx);
				s[2] = Tx | ((wc >> 3*Bitx) & Maskx);
				s[3] = Tx | ((wc >> 2*Bitx) & Maskx);
				s[4] = Tx | ((wc >> 1*Bitx) & Maskx);
				s[5] = Tx |  (wc & Maskx);
				return 6;
			}
			/* 5 bytes */
			s[0] = T5 |  (wc >> 4*Bitx);
			s[1] = Tx | ((wc >> 3*Bitx) & Maskx);
			s[2] = Tx | ((wc >> 2*Bitx) & Maskx);
			s[3] = Tx | ((wc >> 1*Bitx) & Maskx);
			s[4] = Tx |  (wc & Maskx);
			return 5;
		}
		if(wc & ~Wchar3) {
			/* 4 bytes */
			s[0] = T4 |  (wc >> 3*Bitx);
			s[1] = Tx | ((wc >> 2*Bitx) & Maskx);
			s[2] = Tx | ((wc >> 1*Bitx) & Maskx);
			s[3] = Tx |  (wc & Maskx);
			return 4;
		}
		/* 3 bytes */
		s[0] = T3 |  (wc >> 2*Bitx);
		s[1] = Tx | ((wc >> 1*Bitx) & Maskx);
		s[2] = Tx |  (wc & Maskx);
		return 3;
	}
	if(wc & ~Wchar1) {
		/* 2 bytes */
		s[0] = T2 | (wc >> 1*Bitx);
		s[1] = Tx | (wc & Maskx);
		return 2;
	}
	/* 1 byte */
	s[0] = T1 | wc;
	return 1;
}