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bf.go
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bf.go
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// a bf interpreter
package main
import (
"flag"
"fmt"
"os"
)
const (
MemSize = 500000
)
func main() {
flag.Parse()
if flag.NArg() < 1 {
die("usage: <file>")
}
run(flag.Arg(0))
}
func run(fn string) {
code, err := os.ReadFile(fn)
if err != nil {
die("%v", err)
}
ip := 0
mem := make([]byte, MemSize)
for i := 0; i < len(code); i++ {
switch code[i] {
case '>':
if ip++; ip > len(mem) {
nmem := make([]byte, len(mem)*2)
copy(nmem, mem)
mem = nmem
}
case '<':
if ip--; ip < 0 {
nmem := make([]byte, len(mem)*2)
copy(nmem[len(mem):], mem)
ip = len(mem) - 1
}
case '.':
fmt.Printf("%c", mem[ip])
case '+':
mem[ip]++
case '-':
mem[ip]--
case ',':
var r rune
fmt.Scanf("%v", &r)
mem[ip] = byte(r)
case '[':
if mem[ip] == 0 {
for p := 1; p > 0; {
if i++; i >= len(code) {
die("unmatched ]")
}
if code[i] == '[' {
p++
} else if code[i] == ']' {
p--
}
}
}
case ']':
if mem[ip] != 0 {
for p := 1; p > 0; {
if i--; i < 0 {
die("unmatched [")
}
if code[i] == ']' {
p++
} else if code[i] == '[' {
p--
}
}
}
}
}
}
func die(format string, args ...interface{}) {
fmt.Printf(format+"\n", args...)
os.Exit(1)
}