Add a math entropy source

src/sources/index.ts

@@ -30,6 +30,7 @@ import getMonochromeDepth from './monochrome'
 import getContrastPreference from './contrast'
 import isMotionReduced from './reduced_motion'
 import isHDR from './hdr'
+import getMathFingerprint from './math'
 
 /**
  * The list of entropy sources used to make visitor identifiers.
@@ -72,6 +73,7 @@ export const sources = {
   contrast: getContrastPreference,
   reducedMotion: isMotionReduced,
   hdr: isHDR,
+  math: getMathFingerprint,
 }
 
 /**

src/sources/math.test.ts

@@ -0,0 +1,46 @@
+import getMathFingerprint from './math'
+
+const expectedKeys = [
+  'acos',
+  'acosh',
+  'acoshPf',
+  'asin',
+  'asinh',
+  'asinhPf',
+  'atanh',
+  'atanhPf',
+  'atan',
+  'sin',
+  'sinh',
+  'sinhPf',
+  'cos',
+  'cosh',
+  'coshPf',
+  'tan',
+  'tanh',
+  'tanhPf',
+  'exp',
+  'expm1',
+  'expm1Pf',
+  'log1p',
+  'log1pPf',
+  'powPI',
+]
+
+describe('Sources', () => {
+  describe('math', () => {
+    it('works correctly', () => {
+      const data = getMathFingerprint()
+
+      let sum = 0
+
+      for (const key of expectedKeys) {
+        const value = data[key]
+        expect(typeof value).toBe('number')
+        sum += value
+      }
+
+      expect(sum).not.toBe(0)
+    })
+  })
+})

src/sources/math.ts

@@ -0,0 +1,64 @@
+const M = Math // To reduce the minified code size
+const fallbackFn = () => 0
+
+// Native operations
+const acos = M.acos || fallbackFn
+const acosh = M.acosh || fallbackFn
+const asin = M.asin || fallbackFn
+const asinh = M.asinh || fallbackFn
+const atanh = M.atanh || fallbackFn
+const atan = M.atan || fallbackFn
+const sin = M.sin || fallbackFn
+const sinh = M.sinh || fallbackFn
+const cos = M.cos || fallbackFn
+const cosh = M.cosh || fallbackFn
+const tan = M.tan || fallbackFn
+const tanh = M.tanh || fallbackFn
+const exp = M.exp || fallbackFn
+const expm1 = M.expm1 || fallbackFn
+const log1p = M.log1p || fallbackFn
+
+// Operation polyfills
+const powPI = (value: number) => M.pow(M.PI, value)
+const acoshPf = (value: number) => M.log(value + M.sqrt(value * value - 1))
+const asinhPf = (value: number) => M.log(value + M.sqrt(value * value + 1))
+const atanhPf = (value: number) => M.log((1 + value) / (1 - value)) / 2
+const sinhPf = (value: number) => M.exp(value) - 1 / M.exp(value) / 2
+const coshPf = (value: number) => (M.exp(value) + 1 / M.exp(value)) / 2
+const expm1Pf = (value: number) => M.exp(value) - 1
+const tanhPf = (value: number) => (M.exp(2 * value) - 1) / (M.exp(2 * value) + 1)
+const log1pPf = (value: number) => M.log(1 + value)
+
+/**
+ * @see https://gitlab.torproject.org/legacy/trac/-/issues/13018
+ * @see https://bugzilla.mozilla.org/show_bug.cgi?id=531915
+ */
+export default function getMathFingerprint(): Record<string, number> {
+  // Note: constant values are empirical
+  return {
+    acos: acos(0.123124234234234242),
+    acosh: acosh(1e308),
+    acoshPf: acoshPf(1e154), // 1e308 will not work for polyfill
+    asin: asin(0.123124234234234242),
+    asinh: asinh(1),
+    asinhPf: asinhPf(1),
+    atanh: atanh(0.5),
+    atanhPf: atanhPf(0.5),
+    atan: atan(0.5),
+    sin: sin(-1e300),
+    sinh: sinh(1),
+    sinhPf: sinhPf(1),
+    cos: cos(10.000000000123),
+    cosh: cosh(1),
+    coshPf: coshPf(1),
+    tan: tan(-1e300),
+    tanh: tanh(1),
+    tanhPf: tanhPf(1),
+    exp: exp(1),
+    expm1: expm1(1),
+    expm1Pf: expm1Pf(1),
+    log1p: log1p(10),
+    log1pPf: log1pPf(10),
+    powPI: powPI(-100),
+  }
+}