118 lines
2.8 KiB
Go
118 lines
2.8 KiB
Go
// Copyright (C) MongoDB, Inc. 2017-present.
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may
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// not use this file except in compliance with the License. You may obtain
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// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
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package decimal128
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import (
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"strconv"
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)
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// These constants are the maximum and minimum values for the exponent field in a decimal128 value.
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const (
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MaxDecimal128Exp = 6111
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MinDecimal128Exp = -6176
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)
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func divmod(h, l uint64, div uint32) (qh, ql uint64, rem uint32) {
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div64 := uint64(div)
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a := h >> 32
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aq := a / div64
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ar := a % div64
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b := ar<<32 + h&(1<<32-1)
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bq := b / div64
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br := b % div64
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c := br<<32 + l>>32
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cq := c / div64
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cr := c % div64
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d := cr<<32 + l&(1<<32-1)
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dq := d / div64
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dr := d % div64
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return (aq<<32 | bq), (cq<<32 | dq), uint32(dr)
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}
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// String returns a string representation of the decimal value.
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func String(h, l uint64) string {
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var posSign int // positive sign
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var exp int // exponent
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var high, low uint64 // significand high/low
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if h>>63&1 == 0 {
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posSign = 1
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}
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switch h >> 58 & (1<<5 - 1) {
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case 0x1F:
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return "NaN"
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case 0x1E:
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return "-Infinity"[posSign:]
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}
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low = l
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if h>>61&3 == 3 {
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// Bits: 1*sign 2*ignored 14*exponent 111*significand.
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// Implicit 0b100 prefix in significand.
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exp = int(h >> 47 & (1<<14 - 1))
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// Spec says all of these values are out of range.
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high, low = 0, 0
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} else {
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// Bits: 1*sign 14*exponent 113*significand
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exp = int(h >> 49 & (1<<14 - 1))
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high = h & (1<<49 - 1)
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}
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exp += MinDecimal128Exp
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// Would be handled by the logic below, but that's trivial and common.
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if high == 0 && low == 0 && exp == 0 {
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return "-0"[posSign:]
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}
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var repr [48]byte // Loop 5 times over 9 digits plus dot, negative sign, and leading zero.
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var last = len(repr)
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var i = len(repr)
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var dot = len(repr) + exp
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var rem uint32
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Loop:
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for d9 := 0; d9 < 5; d9++ {
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high, low, rem = divmod(high, low, 1e9)
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for d1 := 0; d1 < 9; d1++ {
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// Handle "-0.0", "0.00123400", "-1.00E-6", "1.050E+3", etc.
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if i < len(repr) && (dot == i || low == 0 && high == 0 && rem > 0 && rem < 10 && (dot < i-6 || exp > 0)) {
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exp += len(repr) - i
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i--
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repr[i] = '.'
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last = i - 1
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dot = len(repr) // Unmark.
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}
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c := '0' + byte(rem%10)
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rem /= 10
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i--
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repr[i] = c
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// Handle "0E+3", "1E+3", etc.
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if low == 0 && high == 0 && rem == 0 && i == len(repr)-1 && (dot < i-5 || exp > 0) {
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last = i
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break Loop
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}
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if c != '0' {
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last = i
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}
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// Break early. Works without it, but why.
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if dot > i && low == 0 && high == 0 && rem == 0 {
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break Loop
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}
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}
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}
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repr[last-1] = '-'
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last--
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if exp > 0 {
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return string(repr[last+posSign:]) + "E+" + strconv.Itoa(exp)
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}
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if exp < 0 {
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return string(repr[last+posSign:]) + "E" + strconv.Itoa(exp)
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}
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return string(repr[last+posSign:])
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}
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