ch3¶
basename1/main.go¶
/gopl.io/ch3/basename1/main.go¶
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 72.
// Basename1 reads file names from stdin and prints the base name of each one.
package main
import (
"bufio"
"fmt"
"os"
)
func main() {
input := bufio.NewScanner(os.Stdin)
for input.Scan() {
fmt.Println(basename(input.Text()))
}
// NOTE: ignoring potential errors from input.Err()
}
//!+
// basename removes directory components and a .suffix.
// e.g., a => a, a.go => a, a/b/c.go => c, a/b.c.go => b.c
func basename(s string) string {
// Discard last '/' and everything before.
for i := len(s) - 1; i >= 0; i-- {
if s[i] == '/' {
s = s[i+1:]
break
}
}
// Preserve everything before last '.'.
for i := len(s) - 1; i >= 0; i-- {
if s[i] == '.' {
s = s[:i]
break
}
}
return s
}
//!-
basename2/main.go¶
/gopl.io/ch3/basename2/main.go¶
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 72.
// Basename2 reads file names from stdin and prints the base name of each one.
package main
import (
"bufio"
"fmt"
"os"
"strings"
)
func main() {
input := bufio.NewScanner(os.Stdin)
for input.Scan() {
fmt.Println(basename(input.Text()))
}
// NOTE: ignoring potential errors from input.Err()
}
// basename removes directory components and a trailing .suffix.
// e.g., a => a, a.go => a, a/b/c.go => c, a/b.c.go => b.c
//!+
func basename(s string) string {
slash := strings.LastIndex(s, "/") // -1 if "/" not found
s = s[slash+1:]
if dot := strings.LastIndex(s, "."); dot >= 0 {
s = s[:dot]
}
return s
}
//!-
comma/main.go¶
/gopl.io/ch3/comma/main.go¶
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 73.
// Comma prints its argument numbers with a comma at each power of 1000.
//
// Example:
// $ go build gopl.io/ch3/comma
// $ ./comma 1 12 123 1234 1234567890
// 1
// 12
// 123
// 1,234
// 1,234,567,890
//
package main
import (
"fmt"
"os"
)
func main() {
for i := 1; i < len(os.Args); i++ {
fmt.Printf(" %s\n", comma(os.Args[i]))
}
}
//!+
// comma inserts commas in a non-negative decimal integer string.
func comma(s string) string {
n := len(s)
if n <= 3 {
return s
}
return comma(s[:n-3]) + "," + s[n-3:]
}
//!-
mandelbrot/main.go¶
/gopl.io/ch3/mandelbrot/main.go¶
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 61.
//!+
// Mandelbrot emits a PNG image of the Mandelbrot fractal.
package main
import (
"image"
"image/color"
"image/png"
"math/cmplx"
"os"
)
func main() {
const (
xmin, ymin, xmax, ymax = -2, -2, +2, +2
width, height = 1024, 1024
)
img := image.NewRGBA(image.Rect(0, 0, width, height))
for py := 0; py < height; py++ {
y := float64(py)/height*(ymax-ymin) + ymin
for px := 0; px < width; px++ {
x := float64(px)/width*(xmax-xmin) + xmin
z := complex(x, y)
// Image point (px, py) represents complex value z.
img.Set(px, py, mandelbrot(z))
}
}
png.Encode(os.Stdout, img) // NOTE: ignoring errors
}
func mandelbrot(z complex128) color.Color {
const iterations = 200
const contrast = 15
var v complex128
for n := uint8(0); n < iterations; n++ {
v = v*v + z
if cmplx.Abs(v) > 2 {
return color.Gray{255 - contrast*n}
}
}
return color.Black
}
//!-
// Some other interesting functions:
func acos(z complex128) color.Color {
v := cmplx.Acos(z)
blue := uint8(real(v)*128) + 127
red := uint8(imag(v)*128) + 127
return color.YCbCr{192, blue, red}
}
func sqrt(z complex128) color.Color {
v := cmplx.Sqrt(z)
blue := uint8(real(v)*128) + 127
red := uint8(imag(v)*128) + 127
return color.YCbCr{128, blue, red}
}
// f(x) = x^4 - 1
//
// z' = z - f(z)/f'(z)
// = z - (z^4 - 1) / (4 * z^3)
// = z - (z - 1/z^3) / 4
func newton(z complex128) color.Color {
const iterations = 37
const contrast = 7
for i := uint8(0); i < iterations; i++ {
z -= (z - 1/(z*z*z)) / 4
if cmplx.Abs(z*z*z*z-1) < 1e-6 {
return color.Gray{255 - contrast*i}
}
}
return color.Black
}
netflag/netflag.go¶
/gopl.io/ch3/netflag/netflag.go¶
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 77.
// Netflag demonstrates an integer type used as a bit field.
package main
import (
"fmt"
. "net"
)
//!+
func IsUp(v Flags) bool { return v&FlagUp == FlagUp }
func TurnDown(v *Flags) { *v &^= FlagUp }
func SetBroadcast(v *Flags) { *v |= FlagBroadcast }
func IsCast(v Flags) bool { return v&(FlagBroadcast|FlagMulticast) != 0 }
func main() {
var v Flags = FlagMulticast | FlagUp
fmt.Printf("%b %t\n", v, IsUp(v)) // "10001 true"
TurnDown(&v)
fmt.Printf("%b %t\n", v, IsUp(v)) // "10000 false"
SetBroadcast(&v)
fmt.Printf("%b %t\n", v, IsUp(v)) // "10010 false"
fmt.Printf("%b %t\n", v, IsCast(v)) // "10010 true"
}
//!-
printints/main.go¶
/gopl.io/ch3/printints/main.go¶
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 74.
// Printints demonstrates the use of bytes.Buffer to format a string.
package main
import (
"bytes"
"fmt"
)
//!+
// intsToString is like fmt.Sprint(values) but adds commas.
func intsToString(values []int) string {
var buf bytes.Buffer
buf.WriteByte('[')
for i, v := range values {
if i > 0 {
buf.WriteString(", ")
}
fmt.Fprintf(&buf, "%d", v)
}
buf.WriteByte(']')
return buf.String()
}
func main() {
fmt.Println(intsToString([]int{1, 2, 3})) // "[1, 2, 3]"
}
//!-
surface/main.go¶
/gopl.io/ch3/surface/main.go¶
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 58.
//!+
// 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
}
//!-