I have been playing with the karatsuba algorithm and was doing some testing
testing to compute the correct values of two large numbers
3141592653589793238462643383279502884197169399375105820974944592
and 2718281828459045235360287471352662497757247093699959574966967627. When
working with the math/big package I noticed this oddity, I am sure I am
doing something wrong but hopefully someone can help point it out. If
notice from below the value out of big.NewFloat(myFloat) does not match the
value from printing out g. It also does not match if I print using
g.Float64() and then print the value from that. Should not this be the same
thing in and the same thing out? Thanks in advance.
//
8539734222673567065463550869546574495034888535765114961879601127067743044893204848617875072216249073013374895871952806582723184
- correct
//
8539734222673566930176750436921930623970378254642185393758656420093500067115747270318696482879857934897660315084890343252951040
- incorrect but this is what I get with the big.NewFloat().Mul
f := big.NewFloat(float64(
3141592653589793238462643383279502884197169399375105820974944592))
//.SetPrec(9223372036854775807)
//.SetMode(big.ToZero)
g := big.NewFloat(float64(
2718281828459045235360287471352662497757247093699959574966967627))
//.SetPrec(9223372036854775807)
//.SetMode(big.ToZero)
2718281828459045271981924443963747209279784634148078442319446016.000000
this is what g prints vs what was input
h := big.NewFloat(1).Mul(f, g).SetPrec(9223372036854775807)
//.SetMode(big.ToZero)
a := float64(
3141592653589793238462643383279502884197169399375105820974944592) * float64(
2718281828459045235360287471352662497757247093699959574966967627)
fmt.Printf("%f\n", f)
fmt.Printf("%f\n", g) //prints out
2718281828459045271981924443963747209279784634148078442319446016.000000
fmt.Printf("%f\n", a)
fmt.Printf("%f\n", h)
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