Merge branch 'fix-float-imprecision' into 'master'

Fix float imprecision

See merge request bloodyhealth/drip!138

lib/sympto/temperature.js

@@ -51,7 +51,7 @@ function checkIfFirstHighMeasurement(temp, i, temperatureDays, ltl) {
 function getResultForRegularRule(nextDaysAfterPotentialFhm, ltl) {
   if (!nextDaysAfterPotentialFhm.every(day => day.temp > ltl)) return false
   const thirdDay = nextDaysAfterPotentialFhm[1]
-  if (rounded(thirdDay.temp - ltl, 0.1) < 0.2) return false
+  if (isLessThan0Point2(thirdDay.temp - ltl)) return false
   return {
     detected: true,
     rule: 0,
@@ -77,7 +77,7 @@ function getResultForSecondExceptionRule(nextDaysAfterPotentialFhm, ltl) {
   if (nextDaysAfterPotentialFhm.length < 3) return false
   if (secondOrThirdTempIsAtOrBelowLtl(nextDaysAfterPotentialFhm, ltl)) {
     const fourthDay = nextDaysAfterPotentialFhm[2]
-    if (rounded(fourthDay.temp - ltl, 0.1) >= 0.2) {
+    if (isBiggerOrEqual0Point2(fourthDay.temp - ltl)) {
       return {
         detected: true,
         rule: 2,
@@ -104,3 +104,19 @@ function rounded(val, step) {
   // we round the difference because of JS decimal weirdness
   return Math.round(val * inverted) / inverted
 }
+
+
+// since we're dealing with floats, there is some imprecision in comparisons,
+// so we add an error margin that is definitely much smaller than any possible
+// actual difference between values
+// see https://floating-point-gui.de/errors/comparison/ for background
+
+const errorMargin = 0.0001
+
+function isLessThan0Point2(val) {
+  return val < (0.2 - errorMargin)
+}
+
+function isBiggerOrEqual0Point2(val) {
+  return val >= (0.2 - errorMargin)
+}
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