Fluke user manual 2620A/2625A, Figure E-1. ASCII String Decoding

2620A/2625A

Users Manual

/*

-* decode(): Decode LOG_BIN? response string into raw byte stream

**

**Decoding is done on multiples of four input bytes:

** 543210 543210 543210 543210 (bit number in ASCII bytes)

**+--------+--------+--------+--------+

** src[0] src[1] src[2] src[3] ASCII string input

**+--------+--------+--------+--------+

**	765432		107654	321076	543210	(bit number in raw bytes)
**	/		/	/
**	/		/	/
**			/	/
**		/		/
**				/
**				/
**
**	76543210	76543210 76543210				(bit number in raw bytes)

**+--------+--------+--------+

** dst[0] dst[1] dst[2] Raw data output

**+--------+--------+--------+

**Inputs:

** dst Destination for binary data (must have enough space

**allocated; the maximum needed is 6 timestamp bytes + 3

**bytes for temp units, measurement rate, and digital I/O

**+ 4 bytes/float * 22 floating point values = 97 bytes).

**	src	Source	ASCII string	(null	terminated)
**
** Outputs:
**	dst	Set to	binary data,	based	on ASCII string
**

**Returns:

**Number of bytes placed in destination buffer

*/

int

decode(dst, src) unsigned char *dst; char *src;

{

/* src	to dst xlate */
static	struct nibtab_s		{
int lindex;
int lmask;
int lshift;
int rindex;
int rmask;
int rshift;
} nibtab[3] = {
/*	left		right */
0,	0x3f, 2,	1,	0x30, 4,	/* dst[0] from src[0] and src[1] */
1,	0x0f, 4,	2,	0x3c, 2,	/* dst[1] from src[1] and src[2] */
2,	0x03, 6,	3,	0x3f, 0,	/* dst[2] from src[2] and src[3] */
};

auto unsigned char n; auto struct nibtab_s *t; auto unsigned char tmpsrc[4]; auto int dst_bytes;

/* Number of bytes created */ dst_bytes = 0;

/* Process src in chunks of four */ while (*src) {

/* Copy source, filing "holes" at end with zeros */ for (n = 0; n < 4; n++) {

if (*src)

tmpsrc[n] = *src++ - ’0’;

else

tmpsrc[n] = 0;

}

/* Mung source into destination */

for (t = nibtab; t < &nibtab[3]; t++) {

*dst = (tmpsrc[t->lindex] & t->lmask) << t->lshift; *dst = (tmpsrc[t->rindex] & t->rmask) >> t->rshift;

dst++;

dst_bytes++;

}

}

return (dst_bytes);

}

Figure E-1. ASCII String Decoding

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