Fix #1813: bug in engineering notation for numbers of function `forma…

…t`, sometimes resulting in needless trailing zeros

HISTORY.md

@@ -3,6 +3,8 @@
 
 # not yet published, version 6.6.3
 
+- Fix #1813: bug in engineering notation for numbers of function `format`,
+  sometimes resulting in needless trailing zeros.
 - Fix #1808: methods `.toNumber()` and `.toNumeric()` not working on a 
   unitless unit.
 - Fix #1645: not being able to use named operators `mod`, `and`, `not`, `or`,

src/utils/number.js

@@ -310,7 +310,8 @@ export function toEngineering (value, precision) {
     return String(value)
   }
 
-  const rounded = roundDigits(splitNumber(value), precision)
+  const split = splitNumber(value)
+  const rounded = roundDigits(split, precision)
 
   const e = rounded.exponent
   const c = rounded.coefficients
@@ -325,17 +326,15 @@ export function toEngineering (value, precision) {
     }
   } else {
     // concatenate coefficients with necessary zeros
-    const significandsDiff = e >= 0 ? e : Math.abs(newExp)
-
-    // add zeros if necessary (for ex: 1e+8)
-    while (c.length - 1 < significandsDiff) {
+    // add zeros if necessary (for example: 1e+8 -> 100e+6)
+    const missingZeros = Math.abs(e - newExp) - (c.length - 1)
+    for (let i = 0; i < missingZeros; i++) {
       c.push(0)
     }
   }
 
   // find difference in exponents
   let expDiff = Math.abs(e - newExp)
-
   let decimalIdx = 1
 
   // push decimal index over by expDiff times

test/unit-tests/function/string/format.test.js

@@ -71,13 +71,18 @@ describe('format', function () {
     })
     it('should format positive three digits to engineering notation', function () {
       assert.strictEqual(math.format(300, { notation: 'engineering' }), '300e+0')
+      assert.strictEqual(math.format(320, { notation: 'engineering' }), '320e+0')
     })
     it('should format positive four digits to engineering notation', function () {
       assert.strictEqual(math.format(3000, { notation: 'engineering' }), '3e+3')
     })
     it('should format positive uneven four digits to engineering notation', function () {
       assert.strictEqual(math.format(3001, { notation: 'engineering' }), '3.001e+3')
     })
+    it('should format a number without trailing zeros to engineering notation', function () {
+      assert.strictEqual(math.format(3010, { notation: 'engineering' }), '3.01e+3')
+      assert.strictEqual(math.format(452550000, { notation: 'engineering' }), '452.55e+6')
+    })
     it('should format positive uneven ten digits to engineering notation', function () {
       assert.strictEqual(math.format(3741293481, { notation: 'engineering' }), '3.741293481e+9')
     })
@@ -89,6 +94,8 @@ describe('format', function () {
     })
     it('should format positive two digit floating point numbers to engineering notation', function () {
       assert.strictEqual(math.format(0.01, { notation: 'engineering' }), '10e-3')
+      assert.strictEqual(math.format(0.011, { notation: 'engineering' }), '11e-3')
+      assert.strictEqual(math.format(0.0111, { notation: 'engineering' }), '11.1e-3')
     })
     it('should format positive three digit floating point numbers to engineering notation', function () {
       assert.strictEqual(math.format(0.003, { notation: 'engineering' }), '3e-3')
@@ -101,6 +108,7 @@ describe('format', function () {
     })
     it('should format negative single digit floating point numbers to engineering notation', function () {
       assert.strictEqual(math.format(-0.1, { notation: 'engineering' }), '-100e-3')
+      assert.strictEqual(math.format(-0.11, { notation: 'engineering' }), '-110e-3')
     })
     it('should format positive floating point number to engineering notation', function () {
       assert.strictEqual(math.format(13308.0333333333, { precision: 11, notation: 'engineering' }), '13.308033333e+3')
@@ -194,13 +202,18 @@ describe('format', function () {
       })
       it('should format positive three digits to engineering notation', function () {
         assert.strictEqual(math.format(bignumber(300), { notation: 'engineering' }), '300e+0')
+        assert.strictEqual(math.format(bignumber(320), { notation: 'engineering' }), '320e+0')
       })
       it('should format positive four digits to engineering notation', function () {
         assert.strictEqual(math.format(bignumber(3000), { notation: 'engineering' }), '3e+3')
       })
       it('should format positive uneven four digits to engineering notation', function () {
         assert.strictEqual(math.format(bignumber(3001), { notation: 'engineering' }), '3.001e+3')
       })
+      it('should format a number without trailing zeros to engineering notation', function () {
+        assert.strictEqual(math.format(bignumber(3010), { notation: 'engineering' }), '3.01e+3')
+        assert.strictEqual(math.format(bignumber(452550000), { notation: 'engineering' }), '452.55e+6')
+      })
       it('should format positive uneven ten digits to engineering notation', function () {
         assert.strictEqual(math.format(bignumber(3741293481), { notation: 'engineering' }), '3.741293481e+9')
       })
@@ -209,9 +222,12 @@ describe('format', function () {
       })
       it('should format positive single digit floating point numbers to engineering notation', function () {
         assert.strictEqual(math.format(bignumber(0.1), { notation: 'engineering' }), '100e-3')
+        assert.strictEqual(math.format(bignumber(0.11), { notation: 'engineering' }), '110e-3')
       })
       it('should format positive two digit floating point numbers to engineering notation', function () {
         assert.strictEqual(math.format(bignumber(0.01), { notation: 'engineering' }), '10e-3')
+        assert.strictEqual(math.format(bignumber(0.011), { notation: 'engineering' }), '11e-3')
+        assert.strictEqual(math.format(bignumber(0.0111), { notation: 'engineering' }), '11.1e-3')
       })
       it('should format positive three digit floating point numbers to engineering notation', function () {
         assert.strictEqual(math.format(bignumber(0.003), { notation: 'engineering' }), '3e-3')