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v/vlib/math/modf.v

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module math
const (
modf_maxpowtwo = 4.503599627370496000e+15
)
// modf returns integer and fractional floating-point numbers
// that sum to f. Both values have the same sign as f.
//
// special cases are:
// modf(±inf) = ±inf, nan
// modf(nan) = nan, nan
pub fn modf(f f64) (f64, f64) {
abs_f := abs(f)
mut i := 0.0
if abs_f >= math.modf_maxpowtwo {
i = f // it must be an integer
} else {
i = abs_f + math.modf_maxpowtwo // shift fraction off right
i -= math.modf_maxpowtwo // shift back without fraction
for i > abs_f { // above arithmetic might round
i -= 1.0 // test again just to be sure
}
if f < 0.0 {
i = -i
}
}
return i, f - i // signed fractional part
}