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< ol class = "chapter" > < li class = "chapter-item expanded affix " > < a href = "../index.html" > Go语言圣经< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface-zh.html" > 译者序< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface.html" > 前言< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1.html" > < strong aria-hidden = "true" > 1.< / strong > 入门< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-01.html" > < strong aria-hidden = "true" > 1.1.< / strong > Hello, World< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-02.html" > < strong aria-hidden = "true" > 1.2.< / strong > 命令行参数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-03.html" > < strong aria-hidden = "true" > 1.3.< / strong > 查找重复的行< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-04.html" > < strong aria-hidden = "true" > 1.4.< / strong > GIF动画< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-05.html" > < strong aria-hidden = "true" > 1.5.< / strong > 获取URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-06.html" > < strong aria-hidden = "true" > 1.6.< / strong > 并发获取多个URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-07.html" > < strong aria-hidden = "true" > 1.7.< / strong > Web服务< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-08.html" > < strong aria-hidden = "true" > 1.8.< / strong > 本章要点< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2.html" > < strong aria-hidden = "true" > 2.< / strong > 程序结构< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-01.html" > < strong aria-hidden = "true" > 2.1.< / strong > 命名< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-02.html" > < strong aria-hidden = "true" > 2.2.< / strong > 声明< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-03.html" > < strong aria-hidden = "true" > 2.3.< / strong > 变量< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-04.html" > < strong aria-hidden = "true" > 2.4.< / strong > 赋值< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-05.html" > < strong aria-hidden = "true" > 2.5.< / strong > 类型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-06.html" > < strong aria-hidden = "true" > 2.6.< / strong > 包和文件< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-07.html" > < strong aria-hidden = "true" > 2.7.< / strong > 作用域< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3.html" > < strong aria-hidden = "true" > 3.< / strong > 基础数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-01.html" > < strong aria-hidden = "true" > 3.1.< / strong > 整型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-02.html" class = "active" > < strong aria-hidden = "true" > 3.2.< / strong > 浮点数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-03.html" > < strong aria-hidden = "true" > 3.3.< / strong > 复数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-04.html" > < strong aria-hidden = "true" > 3.4.< / strong > 布尔型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-05.html" > < strong aria-hidden = "true" > 3.5.< / strong > 字符串< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-06.html" > < strong aria-hidden = "true" > 3.6.< / strong > 常量< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4.html" > < strong aria-hidden = "true" > 4.< / strong > 复合数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-01.html" > < strong aria-hidden = "true" > 4.1.< / strong > 数组< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-02.html" > < strong aria-hidden = "true" > 4.2.< / strong > Slice< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-03.html" > < strong aria-hidden = "true" > 4.3.< / strong > Map< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-04.html" > < strong aria-hidden = "true" > 4.4.< / strong > 结构体< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-05.html" > < strong aria-hidden = "true" > 4.5.<
2022-08-04 06:59:33 +00:00
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2024-06-12 07:20:07 +00:00
< li > < em > Go语言圣经读书笔记(挖坑中...): < a href = "https://github.com/chai2010/gopl-notes-zh" > https://github.com/chai2010/gopl-notes-zh< / a > < / em > < / li >
< li > < em > 凹语言(Go实现, 面向WASM设计): < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
2023-06-26 17:46:27 +00:00
< / ul >
2022-08-04 06:59:33 +00:00
< hr >
< h2 id = "32-浮点数" > < a class = "header" href = "#32-浮点数" > 3.2. 浮点数< / a > < / h2 >
< p > Go语言提供了两种精度的浮点数， ， < / p >
< p > 这些浮点数类型的取值范围可以从很微小到很巨大。浮点数的范围极限值可以在math包找到。常量math.MaxFloat32表示float32能表示的最大数值， ； < / p >
< p > 一个float32类型的浮点数可以提供大约6个十进制数的精度， ； ， ， （ ： ， ； ， ） ： < / p >
< pre > < code class = "language-Go" > var f float32 = 16777216 // 1 < < 24
fmt.Println(f == f+1) // " true" !
< / code > < / pre >
< p > 浮点数的字面值可以直接写小数部分，像这样：< / p >
< pre > < code class = "language-Go" > const e = 2.71828 // (approximately)
< / code > < / pre >
< p > 小数点前面或后面的数字都可能被省略（例如.707或1.） ， ： < / p >
< pre > < code class = "language-Go" > const Avogadro = 6.02214129e23 // 阿伏伽德罗常数
const Planck = 6.62606957e-34 // 普朗克常数
< / code > < / pre >
< p > 用Printf函数的%g参数打印浮点数， ， ， ， （ ） < / p >
< pre > < code class = "language-Go" > for x := 0; x < 8; x++ {
fmt.Printf(" x = %d e^x = %8.3f\n" , x, math.Exp(float64(x)))
}
< / code > < / pre >
< p > 上面代码打印e的幂， ： < / p >
< pre > < code > x = 0 e^x = 1.000
x = 1 e^x = 2.718
x = 2 e^x = 7.389
x = 3 e^x = 20.086
x = 4 e^x = 54.598
x = 5 e^x = 148.413
x = 6 e^x = 403.429
x = 7 e^x = 1096.633
< / code > < / pre >
< p > math包中除了提供大量常用的数学函数外， ： ， ； ， < / p >
< pre > < code class = "language-Go" > var z float64
fmt.Println(z, -z, 1/z, -1/z, z/z) // " 0 -0 +Inf -Inf NaN"
< / code > < / pre >
< p > 函数math.IsNaN用于测试一个数是否是非数NaN， ， ， （ ： ， ， ） ： < / p >
< pre > < code class = "language-Go" > nan := math.NaN()
fmt.Println(nan == nan, nan < nan, nan > nan) // " false false false"
< / code > < / pre >
< p > 如果一个函数返回的浮点数结果可能失败，最好的做法是用单独的标志报告失败，像这样：< / p >
< pre > < code class = "language-Go" > func compute() (value float64, ok bool) {
// ...
if failed {
return 0, false
}
return result, true
}
< / code > < / pre >
< p > 接下来的程序演示了通过浮点计算生成的图形。它是带有两个参数的z = f(x, y)函数的三维形式， （ ） ， ， < code > sqrt(x*x+y*y)< / code > 。< / p >
< p > < img src = "../images/ch3-01.png" alt = "" / > < / p >
< p > < u > < i > gopl.io/ch3/surface< / i > < / u > < / p >
< pre > < code class = "language-Go" > // Surface computes an SVG rendering of a 3-D surface function.
package main
import (
" fmt"
" math"
)
const (
width, height = 600, 320 // canvas size in pixels
cells = 100 // number of grid cells
xyrange = 30.0 // axis ranges (-xyrange..+xyrange)
xyscale = width / 2 / xyrange // pixels per x or y unit
zscale = height * 0.4 // pixels per z unit
angle = math.Pi / 6 // angle of x, y axes (=30°)
)
var sin30, cos30 = math.Sin(angle), math.Cos(angle) // sin(30°), cos(30°)
func main() {
fmt.Printf(" < svg xmlns='http://www.w3.org/2000/svg' " +
" style='stroke: grey; fill: white; stroke-width: 0.7' " +
" width='%d' height='%d'> " , width, height)
for i := 0; i < cells; i++ {
for j := 0; j < cells; j++ {
ax, ay := corner(i+1, j)
bx, by := corner(i, j)
cx, cy := corner(i, j+1)
dx, dy := corner(i+1, j+1)
fmt.Printf(" < polygon points='%g,%g %g,%g %g,%g %g,%g'/> \n" ,
ax, ay, bx, by, cx, cy, dx, dy)
}
}
fmt.Println(" < /svg> " )
}
func corner(i, j int) (float64, float64) {
// Find point (x,y) at corner of cell (i,j).
x := xyrange * (float64(i)/cells - 0.5)
y := xyrange * (float64(j)/cells - 0.5)
// Compute surface height z.
z := f(x, y)
// Project (x,y,z) isometrically onto 2-D SVG canvas (sx,sy).
sx := width/2 + (x-y)*cos30*xyscale
sy := height/2 + (x+y)*sin30*xyscale - z*zscale
return sx, sy
}
func f(x, y float64) float64 {
r := math.Hypot(x, y) // distance from (0,0)
return math.Sin(r) / r
}
< / code > < / pre >
< p > 要注意的是corner函数返回了两个结果， < / p >
< p > 要解释这个程序是如何工作的需要一些基本的几何学知识， ， ， ， < / p >
< p > 第二个坐标系是一个三维的网格浮点坐标(x,y,z)， ， ， < / p >
< p > 第三个坐标系是一个二维的画布，起点(0,0)在左上角。画布中点的坐标用(sx,sy)表示。我们使用等角投影将三维点(x,y,z)投影到二维的画布中。< / p >
< p > < img src = "../images/ch3-02.png" alt = "" / > < / p >
< p > 画布中从远处到右边的点对应较大的x值和较大的y值。并且画布中x和y值越大， < / p >
< p > 对于二维网格中的每一个网格单元， ， ， ， < / p >
< p > < strong > 练习 3.1： < / strong > 如果f函数返回的是无限制的float64值， < polygon > 多边形元素（ ） < / p >
< p > < strong > 练习 3.2： < / strong > 试验math包中其他函数的渲染图形。你是否能输出一个egg box、moguls或a saddle图案?< / p >
< p > < strong > 练习 3.3： < / strong > 根据高度给每个多边形上色，那样峰值部将是红色（#ff0000） ， （ ） < / p >
< p > < strong > 练习 3.4： < / strong > 参考1.7节Lissajous例子的函数， ， ： < / p >
< pre > < code class = "language-Go" > w.Header().Set(" Content-Type" , " image/svg+xml" )
< / code > < / pre >
< p > （ ， ， ） < / p >
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