108 lines
2.1 KiB
Go
108 lines
2.1 KiB
Go
package timestamp
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import (
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_ "embed"
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"golang.org/x/exp/constraints"
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)
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// run this to regenerate (pointlessly) the base 10 array of 0 to 9999
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//go:generate go run ./gen/.
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//go:embed base10k.txt
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var base10k []byte
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const base = 10000
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type T struct{ N uint64 }
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func New[V constraints.Integer](n V) *T { return &T{uint64(n)} }
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func (n *T) Uint64() uint64 { return n.N }
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func (n *T) Int64() int64 { return int64(n.N) }
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func (n *T) Uint16() uint16 { return uint16(n.N) }
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var powers = []*T{
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{1},
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{base},
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{base * base},
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{base * base * base},
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{base * base * base * base},
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}
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const zero = '0'
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const nine = '9'
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func (n *T) Marshal(dst []byte) (b []byte) {
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nn := n.N
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b = dst
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if n.N == 0 {
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b = append(b, '0')
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return
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}
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var i int
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var trimmed bool
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k := len(powers)
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for k > 0 {
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k--
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q := n.N / powers[k].N
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if !trimmed && q == 0 {
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continue
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}
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offset := q * 4
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bb := base10k[offset : offset+4]
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if !trimmed {
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for i = range bb {
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if bb[i] != '0' {
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bb = bb[i:]
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trimmed = true
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break
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}
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}
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}
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b = append(b, bb...)
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n.N = n.N - q*powers[k].N
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}
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n.N = nn
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return
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}
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// Unmarshal reads a string, which must be a positive integer no larger than math.MaxUint64,
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// skipping any non-numeric content before it.
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//
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// Note that leading zeros are not considered valid, but basically no such thing as machine
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// generated JSON integers with leading zeroes. Until this is disproven, this is the fastest way
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// to read a positive json integer, and a leading zero is decoded as a zero, and the remainder
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// returned.
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func (n *T) Unmarshal(b []byte) (r []byte, err error) {
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if len(b) < 1 {
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err = errorf.E("zero length number")
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return
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}
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var sLen int
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if b[0] == zero {
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r = b[1:]
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n.N = 0
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return
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}
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// count the digits
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for ; sLen < len(b) && b[sLen] >= zero && b[sLen] <= nine && b[sLen] != ','; sLen++ {
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}
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if sLen == 0 {
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err = errorf.E("zero length number")
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return
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}
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if sLen > 20 {
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err = errorf.E("too big number for uint64")
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return
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}
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// the length of the string found
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r = b[sLen:]
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b = b[:sLen]
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for _, ch := range b {
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ch -= zero
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n.N = n.N*10 + uint64(ch)
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}
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return
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}
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