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Make getBin and scaleChange methods of expoHistogramDataPoint #4451

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merged 2 commits into from
Aug 17, 2023
Merged

Make getBin and scaleChange methods of expoHistogramDataPoint #4451

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c4bfd73
Make getBin and scaleChange methods of expoHistogramDataPoint
MrAlias Aug 16, 2023
ab87e73
Merge branch 'main' into methods-instead-of-passed-params
MadVikingGod Aug 17, 2023
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24 changes: 12 additions & 12 deletions sdk/metric/internal/aggregate/exponential_histogram.go
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Original file line number Diff line number Diff line change
Expand Up @@ -102,7 +102,7 @@ func (p *expoHistogramDataPoint[N]) record(v N) {
return
}

bin := getBin(absV, p.scale)
bin := p.getBin(absV)

bucket := &p.posBuckets
if v < 0 {
Expand All @@ -111,7 +111,7 @@ func (p *expoHistogramDataPoint[N]) record(v N) {

// If the new bin would make the counts larger than maxScale, we need to
// downscale current measurements.
if scaleDelta := scaleChange(bin, bucket.startBin, len(bucket.counts), p.maxSize); scaleDelta > 0 {
if scaleDelta := p.scaleChange(bin, bucket.startBin, len(bucket.counts)); scaleDelta > 0 {
if p.scale-scaleDelta < expoMinScale {
// With a scale of -10 there is only two buckets for the whole range of float64 values.
// This can only happen if there is a max size of 1.
Expand All @@ -123,27 +123,26 @@ func (p *expoHistogramDataPoint[N]) record(v N) {
p.posBuckets.downscale(scaleDelta)
p.negBuckets.downscale(scaleDelta)

bin = getBin(absV, p.scale)
bin = p.getBin(absV)
}

bucket.record(bin)
}

// getBin returns the bin of the bucket that the value v should be recorded
// into at the given scale.
func getBin(v float64, scale int) int {
// getBin returns the bin v should be recorded into.
func (p *expoHistogramDataPoint[N]) getBin(v float64) int {
frac, exp := math.Frexp(v)
if scale <= 0 {
if p.scale <= 0 {
// Because of the choice of fraction is always 1 power of two higher than we want.
correction := 1
if frac == .5 {
// If v is an exact power of two the frac will be .5 and the exp
// will be one higher than we want.
correction = 2
}
return (exp - correction) >> (-scale)
return (exp - correction) >> (-p.scale)
}
return exp<<scale + int(math.Log(frac)*scaleFactors[scale]) - 1
return exp<<p.scale + int(math.Log(frac)*scaleFactors[p.scale]) - 1
}

// scaleFactors are constants used in calculating the logarithm index. They are
Expand Down Expand Up @@ -172,8 +171,9 @@ var scaleFactors = [21]float64{
math.Ldexp(math.Log2E, 20),
}

// scaleChange returns the magnitude of the scale change needed to fit bin in the bucket.
func scaleChange(bin, startBin, length, maxSize int) int {
// scaleChange returns the magnitude of the scale change needed to fit bin in
// the bucket. If no scale change is needed 0 is returned.
func (p *expoHistogramDataPoint[N]) scaleChange(bin, startBin, length int) int {
if length == 0 {
// No need to rescale if there are no buckets.
return 0
Expand All @@ -187,7 +187,7 @@ func scaleChange(bin, startBin, length, maxSize int) int {
}

count := 0
for high-low >= maxSize {
for high-low >= p.maxSize {
low = low >> 1
high = high >> 1
count++
Expand Down
19 changes: 10 additions & 9 deletions sdk/metric/internal/aggregate/exponential_histogram_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -655,7 +655,8 @@ func TestScaleChange(t *testing.T) {
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
got := scaleChange(tt.args.bin, tt.args.startBin, tt.args.length, tt.args.maxSize)
p := newExpoHistogramDataPoint[float64](tt.args.maxSize, 20, false, false)
got := p.scaleChange(tt.args.bin, tt.args.startBin, tt.args.length)
if got != tt.want {
t.Errorf("scaleChange() = %v, want %v", got, tt.want)
}
Expand Down Expand Up @@ -927,15 +928,15 @@ func FuzzGetBin(f *testing.F) {
t.Skip("skipping test for zero")
}

// GetBin is only used with a range of -10 to 20.
scale = (scale%31+31)%31 - 10

got := getBin(v, scale)
if v <= lowerBound(got, scale) {
t.Errorf("v=%x scale =%d had bin %d, but was below lower bound %x", v, scale, got, lowerBound(got, scale))
p := newExpoHistogramDataPoint[float64](4, 20, false, false)
// scale range is -10 to 20.
p.scale = (scale%31+31)%31 - 10
got := p.getBin(v)
if v <= lowerBound(got, p.scale) {
t.Errorf("v=%x scale =%d had bin %d, but was below lower bound %x", v, p.scale, got, lowerBound(got, p.scale))
}
if v > lowerBound(got+1, scale) {
t.Errorf("v=%x scale =%d had bin %d, but was above upper bound %x", v, scale, got, lowerBound(got+1, scale))
if v > lowerBound(got+1, p.scale) {
t.Errorf("v=%x scale =%d had bin %d, but was above upper bound %x", v, p.scale, got, lowerBound(got+1, p.scale))
}
})
}
Expand Down