mirror of https://github.com/vbatts/go-mtree.git
50 lines
727 B
Go
50 lines
727 B
Go
package mtree
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import (
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"bufio"
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"io"
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)
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const posixPolynomial uint32 = 0x04C11DB7
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// cksum is an implementation of the POSIX CRC algorithm
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func cksum(r io.Reader) (uint32, int, error) {
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in := bufio.NewReader(r)
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count := 0
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var sum uint32
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f := func(b byte) {
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for i := 7; i >= 0; i-- {
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msb := sum & (1 << 31)
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sum = sum << 1
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if msb != 0 {
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sum = sum ^ posixPolynomial
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}
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}
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sum ^= uint32(b)
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}
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for done := false; !done; {
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switch b, err := in.ReadByte(); err {
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case io.EOF:
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done = true
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case nil:
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f(b)
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count++
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default:
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return ^sum, count, err
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}
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}
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for m := count; ; {
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f(byte(m) & 0xff)
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m = m >> 8
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if m == 0 {
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break
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}
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}
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f(0)
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f(0)
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f(0)
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f(0)
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return ^sum, count, nil
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}
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