1 files changed, 80 insertions, 0 deletions
diff --git a/vendor/modernc.org/mathutil/binarylog.go b/vendor/modernc.org/mathutil/binarylog.go
new file mode 100644
index 0000000..5a35c57
--- /dev/null
+++ b/vendor/modernc.org/mathutil/binarylog.go
@@ -0,0 +1,80 @@
+// Copyright (c) 2016 The mathutil 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 mathutil // import "modernc.org/mathutil"
+
+import (
+	"math/big"
+)
+
+type float struct {
+	n           *big.Int
+	fracBits    int
+	maxFracBits int
+}
+
+func newFloat(n *big.Int, fracBits, maxFracBits int) float {
+	f := float{n: n, fracBits: fracBits, maxFracBits: maxFracBits}
+	f.normalize()
+	return f
+}
+
+func (f *float) normalize() {
+	n := f.n.BitLen()
+	if n == 0 {
+		return
+	}
+
+	if n := f.fracBits - f.maxFracBits; n > 0 {
+		bit := f.n.Bit(n - 1)
+		f.n.Rsh(f.n, uint(n))
+		if bit != 0 {
+			f.n.Add(f.n, _1)
+		}
+		f.fracBits -= n
+	}
+
+	var i int
+	for ; f.fracBits > 0 && i <= f.fracBits && f.n.Bit(i) == 0; i++ {
+		f.fracBits--
+	}
+
+	if i != 0 {
+		f.n.Rsh(f.n, uint(i))
+	}
+}
+
+func (f *float) eq1() bool { return f.fracBits == 0 && f.n.BitLen() == 1 }
+func (f *float) ge2() bool { return f.n.BitLen() > f.fracBits+1 }
+
+func (f *float) div2() {
+	f.fracBits++
+	f.normalize()
+}
+
+// BinaryLog computes the binary logarithm of n. The result consists of a
+// characteristic and a mantissa having precision mantissaBits. The value of
+// the binary logarithm is
+//
+//	characteristic + mantissa*(2^-mantissaBits)
+//
+// BinaryLog panics for n <= 0 or mantissaBits < 0.
+func BinaryLog(n *big.Int, mantissaBits int) (characteristic int, mantissa *big.Int) {
+	if n.Sign() <= 0 || mantissaBits < 0 {
+		panic("invalid argument of BinaryLog")
+	}
+
+	characteristic = n.BitLen() - 1
+	mantissa = big.NewInt(0)
+	x := newFloat(n, characteristic, mantissaBits)
+	for ; mantissaBits != 0 && !x.eq1(); mantissaBits-- {
+		x.sqr()
+		mantissa.Lsh(mantissa, 1)
+		if x.ge2() {
+			mantissa.SetBit(mantissa, 0, 1)
+			x.div2()
+		}
+	}
+	return characteristic, mantissa
+}