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d550c4a0b9
At first it wasn't obvious to me why the first check would give a different result to the second. Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
52 lines
1.6 KiB
Go
52 lines
1.6 KiB
Go
// Copyright 2024 The Prometheus Authors
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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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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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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 almost
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import (
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"math"
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"github.com/prometheus/prometheus/model/value"
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)
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var minNormal = math.Float64frombits(0x0010000000000000) // The smallest positive normal value of type float64.
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// Equal returns true if a and b differ by less than their sum
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// multiplied by epsilon, or if both are StaleNaN, or if both are any other NaN.
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func Equal(a, b, epsilon float64) bool {
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// StaleNaN is a special value that is used as staleness maker, and
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// we don't want it to compare equal to any other NaN.
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if value.IsStaleNaN(a) || value.IsStaleNaN(b) {
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return value.IsStaleNaN(a) && value.IsStaleNaN(b)
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}
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// NaN has no equality but for testing we still want to know whether both values
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// are NaN.
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if math.IsNaN(a) && math.IsNaN(b) {
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return true
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}
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// Cf. http://floating-point-gui.de/errors/comparison/
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if a == b {
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return true
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}
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absSum := math.Abs(a) + math.Abs(b)
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diff := math.Abs(a - b)
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if a == 0 || b == 0 || absSum < minNormal {
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return diff < epsilon*minNormal
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}
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return diff/math.Min(absSum, math.MaxFloat64) < epsilon
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}
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