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Diffstat (limited to 'src/math/big/floatexample_test.go')
| -rw-r--r-- | src/math/big/floatexample_test.go | 141 |
1 files changed, 141 insertions, 0 deletions
diff --git a/src/math/big/floatexample_test.go b/src/math/big/floatexample_test.go new file mode 100644 index 0000000..0c6668c --- /dev/null +++ b/src/math/big/floatexample_test.go @@ -0,0 +1,141 @@ +// Copyright 2015 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 big_test + +import ( + "fmt" + "math" + "math/big" +) + +func ExampleFloat_Add() { + // Operate on numbers of different precision. + var x, y, z big.Float + x.SetInt64(1000) // x is automatically set to 64bit precision + y.SetFloat64(2.718281828) // y is automatically set to 53bit precision + z.SetPrec(32) + z.Add(&x, &y) + fmt.Printf("x = %.10g (%s, prec = %d, acc = %s)\n", &x, x.Text('p', 0), x.Prec(), x.Acc()) + fmt.Printf("y = %.10g (%s, prec = %d, acc = %s)\n", &y, y.Text('p', 0), y.Prec(), y.Acc()) + fmt.Printf("z = %.10g (%s, prec = %d, acc = %s)\n", &z, z.Text('p', 0), z.Prec(), z.Acc()) + // Output: + // x = 1000 (0x.fap+10, prec = 64, acc = Exact) + // y = 2.718281828 (0x.adf85458248cd8p+2, prec = 53, acc = Exact) + // z = 1002.718282 (0x.faadf854p+10, prec = 32, acc = Below) +} + +func ExampleFloat_shift() { + // Implement Float "shift" by modifying the (binary) exponents directly. + for s := -5; s <= 5; s++ { + x := big.NewFloat(0.5) + x.SetMantExp(x, x.MantExp(nil)+s) // shift x by s + fmt.Println(x) + } + // Output: + // 0.015625 + // 0.03125 + // 0.0625 + // 0.125 + // 0.25 + // 0.5 + // 1 + // 2 + // 4 + // 8 + // 16 +} + +func ExampleFloat_Cmp() { + inf := math.Inf(1) + zero := 0.0 + + operands := []float64{-inf, -1.2, -zero, 0, +1.2, +inf} + + fmt.Println(" x y cmp") + fmt.Println("---------------") + for _, x64 := range operands { + x := big.NewFloat(x64) + for _, y64 := range operands { + y := big.NewFloat(y64) + fmt.Printf("%4g %4g %3d\n", x, y, x.Cmp(y)) + } + fmt.Println() + } + + // Output: + // x y cmp + // --------------- + // -Inf -Inf 0 + // -Inf -1.2 -1 + // -Inf -0 -1 + // -Inf 0 -1 + // -Inf 1.2 -1 + // -Inf +Inf -1 + // + // -1.2 -Inf 1 + // -1.2 -1.2 0 + // -1.2 -0 -1 + // -1.2 0 -1 + // -1.2 1.2 -1 + // -1.2 +Inf -1 + // + // -0 -Inf 1 + // -0 -1.2 1 + // -0 -0 0 + // -0 0 0 + // -0 1.2 -1 + // -0 +Inf -1 + // + // 0 -Inf 1 + // 0 -1.2 1 + // 0 -0 0 + // 0 0 0 + // 0 1.2 -1 + // 0 +Inf -1 + // + // 1.2 -Inf 1 + // 1.2 -1.2 1 + // 1.2 -0 1 + // 1.2 0 1 + // 1.2 1.2 0 + // 1.2 +Inf -1 + // + // +Inf -Inf 1 + // +Inf -1.2 1 + // +Inf -0 1 + // +Inf 0 1 + // +Inf 1.2 1 + // +Inf +Inf 0 +} + +func ExampleRoundingMode() { + operands := []float64{2.6, 2.5, 2.1, -2.1, -2.5, -2.6} + + fmt.Print(" x") + for mode := big.ToNearestEven; mode <= big.ToPositiveInf; mode++ { + fmt.Printf(" %s", mode) + } + fmt.Println() + + for _, f64 := range operands { + fmt.Printf("%4g", f64) + for mode := big.ToNearestEven; mode <= big.ToPositiveInf; mode++ { + // sample operands above require 2 bits to represent mantissa + // set binary precision to 2 to round them to integer values + f := new(big.Float).SetPrec(2).SetMode(mode).SetFloat64(f64) + fmt.Printf(" %*g", len(mode.String()), f) + } + fmt.Println() + } + + // Output: + // x ToNearestEven ToNearestAway ToZero AwayFromZero ToNegativeInf ToPositiveInf + // 2.6 3 3 2 3 2 3 + // 2.5 2 3 2 3 2 3 + // 2.1 2 2 2 3 2 3 + // -2.1 -2 -2 -2 -3 -3 -2 + // -2.5 -2 -3 -2 -3 -3 -2 + // -2.6 -3 -3 -2 -3 -3 -2 +} |