73 lines
1.3 KiB
Go
73 lines
1.3 KiB
Go
package strconv
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import (
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"math"
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)
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// ParseDecimal parses number of the format 1.2
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func ParseDecimal(b []byte) (float64, int) {
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// float64 has up to 17 significant decimal digits and an exponent in [-1022,1023]
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i := 0
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//sign := 1.0
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//if 0 < len(b) && b[0] == '-' {
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// sign = -1.0
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// i++
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//}
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start := -1
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dot := -1
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n := uint64(0)
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for ; i < len(b); i++ {
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// parse up to 18 significant digits (with dot will be 17) ignoring zeros before/after
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c := b[i]
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if '0' <= c && c <= '9' {
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if start == -1 {
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if '1' <= c && c <= '9' {
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n = uint64(c - '0')
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start = i
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}
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} else if i-start < 18 {
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n *= 10
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n += uint64(c - '0')
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}
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} else if c == '.' {
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if dot != -1 {
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break
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}
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dot = i
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} else {
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break
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}
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}
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if i == 1 && dot == 0 {
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return 0.0, 0 // only dot
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} else if start == -1 {
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return 0.0, i // only zeros and dot
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} else if dot == -1 {
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dot = i
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}
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exp := (dot - start) - LenUint(n)
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if dot < start {
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exp++
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}
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if 1023 < exp {
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return math.Inf(1), i
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//if sign == 1.0 {
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// return math.Inf(1), i
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//} else {
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// return math.Inf(-1), i
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//}
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} else if exp < -1022 {
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return 0.0, i
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}
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f := float64(n) // sign * float64(n)
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if 0 <= exp && exp < 23 {
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return f * float64pow10[exp], i
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} else if 23 < exp && exp < 0 {
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return f / float64pow10[exp], i
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}
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return f * math.Pow10(exp), i
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}
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