BitOrder

SetReg.c

#include <stdio.h>
#include <stdlib.h>

typedef struct tag_RegisterBlock {
	unsigned char addr;
	int           sbit;
	int           len;
} TRegisterBlock;

static inline void dec2bin(unsigned char val)
{
	char binstr[9] = "";
	binstr[8] = '\0';
	int i;
	for (i=7; i>=0; i--) {
		binstr[i] = (val & 0x01) ? ('1') : ('0');
		val >>= 1;
	}
	printf("%s ", binstr);
}

static inline void setreg(const TRegisterBlock *reg, const unsigned int data)
{
	const int   QUOTIENT = reg->sbit >> 3;
	unsigned int    addr = reg->addr + QUOTIENT;
	int              sft = reg->sbit - QUOTIENT*8;
	int               sz = reg->len;
	unsigned int       d = data << sft;
	unsigned char map[4] = {0xFF, 0xFF, 0xFF, 0xFF};

	{
		int i;
		printf("\n-> map: ");
		for (i=3; i>=0; i--) { printf("%02X ", map[i]); }
		printf("\n");
	}

	while (sz > 0) {
		unsigned char mask = (~(0xFF << sz)) << sft;
		printf("0x%02X | 0x%02X, d=0x%02X:mask=0x%02X\n", (map[addr] & ~mask), (d & mask), d, mask);
		map[addr] = (map[addr] & ~mask) | (d & mask);
		printf("map[%d]=%02X\t(sft=%2d, sz=%2d, d=0x%08X, mask=0x%02X)\n", addr, map[addr], sft, sz, d, mask);
		sz -= (8 - sft);
		sft = 0;
		addr++;
		d >>= 8;
	}

	{
		int i;
		printf("\n-> map: ");
		for (i=3; i>=0; i--) { printf("%02X ", map[i]); }
		printf("\n\n");
		printf("MSB --------------------------- LSB\n");
		for (i=3; i>=0; i--) { dec2bin(map[i]); }
		printf("\n");
	}
}

int main(int argc, char *argv[])
{
	if (argc < 4) {
		printf("require 3 argments. startbit, length, data.\n");
		return -1;
	}

	const TRegisterBlock reg = {
		.addr = 0,
		.sbit = (int)atoi(argv[1]),
		.len  = (int)atoi(argv[2]),
	};
	const unsigned int data = strtoul(argv[3], NULL, 0);
	setreg(&reg, data);

	return 0;
}

./a.out $STARTBIT $BITLENGTH $SETDATA