78 lines
1.9 KiB
Go
78 lines
1.9 KiB
Go
// Copyright 2015 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package types
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import (
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"math"
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)
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// RoundFloat rounds float val to the nearest integer value with float64 format, like GNU rint function.
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// RoundFloat uses default rounding mode, see http://www.gnu.org/software/libc/manual/html_node/Rounding.html
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// so we will choose the even number if the result is midway between two representable value.
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// e.g, 1.5 -> 2, 2.5 -> 2.
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func RoundFloat(val float64) float64 {
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v, frac := math.Modf(val)
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if val >= 0.0 {
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if frac > 0.5 || (frac == 0.5 && uint64(v)%2 != 0) {
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v += 1.0
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}
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} else {
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if frac < -0.5 || (frac == -0.5 && uint64(v)%2 != 0) {
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v -= 1.0
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}
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}
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return v
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}
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func getMaxFloat(flen int, decimal int) float64 {
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intPartLen := flen - decimal
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f := math.Pow10(intPartLen)
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f -= math.Pow10(-decimal)
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return f
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}
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func truncateFloat(f float64, decimal int) float64 {
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pow := math.Pow10(decimal)
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t := (f - math.Floor(f)) * pow
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round := RoundFloat(t)
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f = math.Floor(f) + round/pow
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return f
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}
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// TruncateFloat tries to truncate f.
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// If the result exceeds the max/min float that flen/decimal allowed, returns the max/min float allowed.
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func TruncateFloat(f float64, flen int, decimal int) (float64, error) {
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if math.IsNaN(f) {
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// nan returns 0
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return 0, nil
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}
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maxF := getMaxFloat(flen, decimal)
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if !math.IsInf(f, 0) {
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f = truncateFloat(f, decimal)
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}
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if f > maxF {
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f = maxF
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} else if f < -maxF {
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f = -maxF
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}
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return f, nil
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}
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