MakeFloat

main.m

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // -358974.27
        
        unsigned val = 0;
        
        // set negative bit
        val |= (1 << 31);
        
        NSLog(@"0x%x", val);
        
//        float a = 358974.27;
//        int i = 0;
//        while (a >= 2) {
//            a = a / 2;
//            i ++;
//        }
        
        // i = 18
        // exponent = 18
        // biased = 18 + 127
        // 8 bits for exponent
        val |= (18 + 127) << 23;
        
        NSLog(@"0x%x", val);
        
//        unsigned n = 358974;
//        int l = sizeof(n) * 8;
//        for (int i = l - 1 ; i >= 0; i--) {
//            printf("%x", (n & (1 << i)) >> i);
//        }
        
        // 00000000000001010111101000111110
        
//        float a = 0.27;
//        int i = 0;
//        while (i < 32) {
//            i ++;
//            float d = exp2f(-i);
//            if (a >= d) {
//                a -= d;
//                printf("%x", 1);
//
//                if (a == d) {
//                    break;
//                }
//            }
//            else {
//                printf("%x", 0);
//            }
//        }
        // .01000101000111101011100010000000

        // 1010111101000111110.0100010100011110101110001
        // chop off the most significant bit, because
        // we know it will always be one,
        // and throw out the decimal point,
        // and then round to 23 bits
        // 010111101000111110010001 ~> 01011110100011111001001
        // 010 1111 0100 0111 1100 1001
        // 0x2F47C9
        
        val |= 0x2F47C9;
//        NSLog(@"%@", @(0x2F47C9));
        
        NSLog(@"Our number is %f, and we wanted %f\n", *(float*)&val, -358974.27f);
        // Our number is -358974.281250, and we wanted -358974.281250
    }
    return 0;
}