24bit isa number encoding

#include <stdio.h>
#include <stdint.h>
#include <assert.h>
#include <limits.h>

// 4 bit xor
// 4 bit position
// 16 bit integer / pattern

uint32_t encode(uint64_t v) {
    uint16_t pattern = 0;
    
    for(size_t i = 0; i < 4; ++i) {
        uint16_t segment = v >> (i * 16);
        
        if(segment != 0 &&
            segment != 0xFFFF &&
            segment != pattern &&
            segment != (pattern ^ 0xFFFF)) {
            assert(pattern == 0 && "Unable to encode number");
            pattern = segment;
        }
    }
    
    uint32_t result = pattern;
    
    for(size_t i = 0; i < 4; ++i) {
        uint16_t segment = v >> (i * 16);
        if(segment == 0) {
            
        } else if(segment == 0xFFFF) {
            result |= 0x100000 << i;
        } else if(segment == pattern) {
            result |= 0x010000 << i;
        } else if(segment == (pattern ^ 0xFFFF)) {
            result |= (0x010000 << i) | (0x100000 << i);
        } else {
            assert(0 && "This should never happen");
        }
    }
    
    return result;
}

uint64_t decode(uint32_t v) {
    uint64_t result = 0;
    
    for(size_t i = 0; i < 4; ++i) {
        uint16_t segment = ((0x010000 << i) & v) ? (uint16_t)v : 0;
        segment ^= ((0x100000 << i) & v) ? 0xFFFF : 0;
        
        result |= (uint64_t)segment << (i * 16);
    }
    
    return result;
}

int main(void) {
    uint64_t v = 0x60019FFEFFFF0000;
    //uint64_t v = INT_MIN;
    printf("%lx\n", v);
    //return 0;
    //uint64_t v = -255;
    uint32_t e = encode(v);
    uint64_t d = decode(e);
    printf("%lx\n", d);
    assert(v == d);
    printf("encoded: %x\n", e);
    return 0;
}