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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package math

const (
        uvnan    = 0x7FF0000000000001
        uvinf    = 0x7FF0000000000000
        uvneginf = 0xFFF0000000000000
        mask     = 0x7FF
        shift    = 64 - 11 - 1
        bias     = 1023
)

// Inf returns positive infinity if sign >= 0, negative infinity if sign < 0.
func Inf(sign int) float64 {
        var v uint64
        if sign >= 0 {
                v = uvinf
        } else {
                v = uvneginf
        }
        return Float64frombits(v)
}

// NaN returns an IEEE 754 ``not-a-number'' value.
func NaN() float64 { return Float64frombits(uvnan) }

// IsNaN returns whether f is an IEEE 754 ``not-a-number'' value.
func IsNaN(f float64) (is bool) {
        // IEEE 754 says that only NaNs satisfy f != f.
        // To avoid the floating-point hardware, could use:
        //      x := Float64bits(f);
        //      return uint32(x>>shift)&mask == mask && x != uvinf && x != uvneginf
        return f != f
}

// IsInf returns whether f is an infinity, according to sign.
// If sign > 0, IsInf returns whether f is positive infinity.
// If sign < 0, IsInf returns whether f is negative infinity.
// If sign == 0, IsInf returns whether f is either infinity.
func IsInf(f float64, sign int) bool {
        // Test for infinity by comparing against maximum float.
        // To avoid the floating-point hardware, could use:
        //      x := Float64bits(f);
        //      return sign >= 0 && x == uvinf || sign <= 0 && x == uvneginf;
        return sign >= 0 && f > MaxFloat64 || sign <= 0 && f < -MaxFloat64
}

// normalize returns a normal number y and exponent exp
// satisfying x == y × 2**exp. It assumes x is finite and non-zero.
func normalize(x float64) (y float64, exp int) {
        const SmallestNormal = 2.2250738585072014e-308 // 2**-1022
        if Abs(x) < SmallestNormal {
                return x * (1 << 52), -52
        }
        return x, 0
}