Pack 4 ASCII Nucleotides into 1 byte

pack.cc

#include <cstring>
#include <cstdint>
#include <cstdio>

uint8_t pack_a(const char *cs) {
	uint32_t u;
	memcpy(&u,cs,4);
	u &= 0x06060606;
	u = (u | (u << 6) | (u << 12) | (u << 18)) >> 19;
	return u;
}

uint8_t pack_b(const char *cs) {
	uint32_t u;
	memcpy(&u,cs,4);
	u &= 0x06060606;
	u *= 0x041041;
	u /= 0x80000;
	return u;
}

uint8_t pack_c(const char *cs) {
	uint32_t u;
	memcpy(&u,cs,4);
	return ((u & 0x06060606) * 0x041041)/0x80000;
}

void unpack(int x, char *cs) {
	const char ss[] = "ACTG";
	for(int i=0;i<4;++i) {
		cs[i] = ss[x & 0x3];
		x = x >> 2;
	}
}

int main(int argc, char *argv[] ) {
	char buffer[5] = "NNNN";
	int failures=0;
	for(int b=0;b<256;++b) {
		unpack(b,buffer);
		uint32_t x = pack_c(buffer);
		if(x != b)
			failures += 1;
		printf("%s\t0x%x\t0x%x\t%s\n",buffer,b,x,((x==b) ? "Pass" : "Fail"));
	}
	printf("Total failures: %d\n", failures);
	return 0;
}