@opentelemetry/sdk-metrics
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JavaScript
/*
* Copyright The OpenTelemetry Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import * as ieee754 from './ieee754';
import * as util from '../util';
import { MappingError } from './types';
/**
* LogarithmMapping implements exponential mapping functions for scale > 0.
* For scales <= 0 the exponent mapping should be used.
*/
export class LogarithmMapping {
_scale;
_scaleFactor;
_inverseFactor;
constructor(scale) {
this._scale = scale;
this._scaleFactor = util.ldexp(Math.LOG2E, scale);
this._inverseFactor = util.ldexp(Math.LN2, -scale);
}
/**
* Maps positive floating point values to indexes corresponding to scale
* @param value
* @returns {number} index for provided value at the current scale
*/
mapToIndex(value) {
if (value <= ieee754.MIN_VALUE) {
return this._minNormalLowerBoundaryIndex() - 1;
}
// exact power of two special case
if (ieee754.getSignificand(value) === 0) {
const exp = ieee754.getNormalBase2(value);
return (exp << this._scale) - 1;
}
// non-power of two cases. use Math.floor to round the scaled logarithm
const index = Math.floor(Math.log(value) * this._scaleFactor);
const maxIndex = this._maxNormalLowerBoundaryIndex();
if (index >= maxIndex) {
return maxIndex;
}
return index;
}
/**
* Returns the lower bucket boundary for the given index for scale
*
* @param index
* @returns {number}
*/
lowerBoundary(index) {
const maxIndex = this._maxNormalLowerBoundaryIndex();
if (index >= maxIndex) {
if (index === maxIndex) {
return 2 * Math.exp((index - (1 << this._scale)) / this._scaleFactor);
}
throw new MappingError(`overflow: ${index} is > maximum lower boundary: ${maxIndex}`);
}
const minIndex = this._minNormalLowerBoundaryIndex();
if (index <= minIndex) {
if (index === minIndex) {
return ieee754.MIN_VALUE;
}
else if (index === minIndex - 1) {
return Math.exp((index + (1 << this._scale)) / this._scaleFactor) / 2;
}
throw new MappingError(`overflow: ${index} is < minimum lower boundary: ${minIndex}`);
}
return Math.exp(index * this._inverseFactor);
}
/**
* The scale used by this mapping
* @returns {number}
*/
get scale() {
return this._scale;
}
_minNormalLowerBoundaryIndex() {
return ieee754.MIN_NORMAL_EXPONENT << this._scale;
}
_maxNormalLowerBoundaryIndex() {
return ((ieee754.MAX_NORMAL_EXPONENT + 1) << this._scale) - 1;
}
}
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