49 lines
842 B
Go
49 lines
842 B
Go
//go:build purego || !amd64
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// +build purego !amd64
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package ascii
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import (
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"unsafe"
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)
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// ValidString returns true if s contains only ASCII characters.
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func ValidString(s string) bool {
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p := *(*unsafe.Pointer)(unsafe.Pointer(&s))
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i := uintptr(0)
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n := uintptr(len(s))
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for i+8 <= n {
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if (*(*uint64)(unsafe.Pointer(uintptr(p) + i)) & 0x8080808080808080) != 0 {
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return false
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}
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i += 8
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}
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if i+4 <= n {
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if (*(*uint32)(unsafe.Pointer(uintptr(p) + i)) & 0x80808080) != 0 {
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return false
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}
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i += 4
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}
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if i == n {
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return true
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}
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p = unsafe.Pointer(uintptr(p) + i)
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var x uint32
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switch n - i {
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case 3:
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x = uint32(*(*uint16)(p)) | uint32(*(*uint8)(unsafe.Pointer(uintptr(p) + 2)))<<16
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case 2:
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x = uint32(*(*uint16)(p))
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case 1:
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x = uint32(*(*uint8)(p))
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default:
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return true
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}
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return (x & 0x80808080) == 0
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}
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