Fix josdejong#1512: bug in format notation engineering

josdejong · josdejong · commit 0a6aded52a6b · 2019-05-16T21:51:13.000+02:00
diff --git a/HISTORY.md b/HISTORY.md
@@ -1,6 +1,13 @@
 # History
 
 
+# not yet published, version 5.10.1
+
+- Fix #1512: format using notation `engineering` can give wrong results
+  when the value has less significant digits than the number of digits in
+  the output.
+
+
 # 2019-05-08, version 5.10.0
 
 - Fix `lib/header.js` not having filled in date and version. Thanks @kevjin.
diff --git a/src/utils/bignumber/formatter.js b/src/utils/bignumber/formatter.js
@@ -174,11 +174,14 @@ exports.toEngineering = function (value, precision) {
   const newExp = e % 3 === 0 ? e : (e < 0 ? (e - 3) - (e % 3) : e - (e % 3))
 
   // find difference in exponents, and calculate the value without exponent
-  const expDiff = Math.abs(e - newExp)
-  const valueWithoutExp = value.mul(Math.pow(10, expDiff - e))
+  const valueWithoutExp = value.mul(Math.pow(10, -newExp))
 
-  return valueWithoutExp.toPrecision(precision).toString() +
-    'e' + (e >= 0 ? '+' : '') + newExp.toString()
+  let valueStr = valueWithoutExp.toPrecision(precision)
+  if (valueStr.indexOf('e') !== -1) {
+    valueStr = valueWithoutExp.toString()
+  }
+
+  return valueStr + 'e' + (e >= 0 ? '+' : '') + newExp.toString()
 }
 
 /**
diff --git a/src/utils/number.js b/src/utils/number.js
@@ -263,13 +263,17 @@ exports.toEngineering = function (value, precision) {
 
   if (exports.isNumber(precision)) {
     // add zeroes to give correct sig figs
-    if (precision > c.length) c = c.concat(zeros(precision - c.length))
+    while (precision > c.length || (e - newExp) + 1 > c.length) {
+      c.push(0)
+    }
   } else {
     // concatenate coefficients with necessary zeros
     const significandsDiff = e >= 0 ? e : Math.abs(newExp)
 
     // add zeros if necessary (for ex: 1e+8)
-    if (c.length - 1 < significandsDiff) c = c.concat(zeros(significandsDiff - (c.length - 1)))
+    while (c.length - 1 < significandsDiff) {
+      c.push(0)
+    }
   }
 
   // find difference in exponents
@@ -278,7 +282,10 @@ exports.toEngineering = function (value, precision) {
   let decimalIdx = 1
 
   // push decimal index over by expDiff times
-  while (--expDiff >= 0) decimalIdx++
+  while (expDiff > 0) {
+    decimalIdx++
+    expDiff--
+  }
 
   // if all coefficient values are zero after the decimal point and precision is unset, don't add a decimal value.
   // otherwise concat with the rest of the coefficients
diff --git a/test/function/string/format.test.js b/test/function/string/format.test.js
@@ -119,6 +119,19 @@ describe('format', function () {
       assert.strictEqual(math.format(0.000124, { notation: 'engineering', precision: 4 }), '124.0e-6')
       assert.strictEqual(math.format(0.000124, { notation: 'engineering', precision: 3 }), '124e-6')
       assert.strictEqual(math.format(1.24, { notation: 'engineering', precision: 3 }), '1.24e+0')
+
+      // less significant figures than precision, need to add zeros
+      assert.strictEqual(math.format(10e3, { notation: 'engineering', precision: 2 }), '10e+3')
+      assert.strictEqual(math.format(10e3, { notation: 'engineering', precision: 1 }), '10e+3')
+      assert.strictEqual(math.format(100e3, { notation: 'engineering', precision: 2 }), '100e+3')
+      assert.strictEqual(math.format(100e3, { notation: 'engineering', precision: 1 }), '100e+3')
+      assert.strictEqual(math.format(100, { notation: 'engineering', precision: 2 }), '100e+0')
+      assert.strictEqual(math.format(10, { notation: 'engineering', precision: 2 }), '10e+0')
+      assert.strictEqual(math.format(10, { notation: 'engineering', precision: 1 }), '10e+0')
+      assert.strictEqual(math.format(1, { notation: 'engineering', precision: 2 }), '1.0e+0')
+      assert.strictEqual(math.format(10e-3, { notation: 'engineering', precision: 2 }), '10e-3')
+      assert.strictEqual(math.format(100e-3, { notation: 'engineering', precision: 2 }), '100e-3')
+      assert.strictEqual(math.format(100e-3, { notation: 'engineering', precision: 1 }), '100e-3')
     })
   })
 
@@ -201,6 +214,19 @@ describe('format', function () {
         assert.strictEqual(math.format(bignumber(0.000124), { notation: 'engineering', precision: 4 }), '124.0e-6')
         assert.strictEqual(math.format(bignumber(0.000124), { notation: 'engineering', precision: 3 }), '124e-6')
         assert.strictEqual(math.format(bignumber(1.24), { notation: 'engineering', precision: 3 }), '1.24e+0')
+
+        // less significant figures than precision, need to add zeros
+        assert.strictEqual(math.format(bignumber(10e3), { notation: 'engineering', precision: 2 }), '10e+3')
+        assert.strictEqual(math.format(bignumber(10e3), { notation: 'engineering', precision: 1 }), '10e+3')
+        assert.strictEqual(math.format(bignumber(100e3), { notation: 'engineering', precision: 2 }), '100e+3')
+        assert.strictEqual(math.format(bignumber(100e3), { notation: 'engineering', precision: 1 }), '100e+3')
+        assert.strictEqual(math.format(bignumber(100), { notation: 'engineering', precision: 2 }), '100e+0')
+        assert.strictEqual(math.format(bignumber(10), { notation: 'engineering', precision: 2 }), '10e+0')
+        assert.strictEqual(math.format(bignumber(10), { notation: 'engineering', precision: 1 }), '10e+0')
+        assert.strictEqual(math.format(bignumber(1), { notation: 'engineering', precision: 2 }), '1.0e+0')
+        assert.strictEqual(math.format(bignumber(10e-3), { notation: 'engineering', precision: 2 }), '10e-3')
+        assert.strictEqual(math.format(bignumber(100e-3), { notation: 'engineering', precision: 2 }), '100e-3')
+        assert.strictEqual(math.format(bignumber(100e-3), { notation: 'engineering', precision: 1 }), '100e-3')
       })
     })
   })
