fix(fmod): fmod computes the mod operation with raw arithmetic

fixes #15
mauriciopoppe · Feb 16, 2018 · 0133e47 · 0133e47
1 parent fe7a842
commit 0133e47
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Showing 4 changed files with 21 additions and 1 deletion.
diff --git a/lib/interval.js b/lib/interval.js
@@ -231,6 +231,7 @@ Interval.prototype.setWhole = function () {
  * @return {Interval} The calling interval
  */
 Interval.prototype.open = function (lo, hi) {
+console.log(lo, hi)
   return this.assign(round.safeNext(lo), round.safePrev(hi))
 }
 

diff --git a/lib/operations/algebra.js b/lib/operations/algebra.js
@@ -23,11 +23,14 @@ var algebra = {}
  *   Interval(5.3, 5.3),
  *   Interval(2, 2)
  * ) // Interval(1.3, 1.3)
+ *
  * @example
  * Interval.fmod(
  *   Interval(5, 7),
  *   Interval(2, 3)
  * ) // Interval(2, 5)
+ * // explanation: [5, 7] - [2, 3] * 1 = [2, 5]
+ *
  * @param {Interval} x
  * @param {Interval} y
  * @return {Interval}
@@ -37,7 +40,9 @@ algebra.fmod = function (x, y) {
     return constants.EMPTY
   }
   var yb = x.lo < 0 ? y.lo : y.hi
-  var n = rmath.intLo(rmath.divLo(x.lo, yb))
+  var n = x.lo / yb
+  if (n < 0) n = Math.ceil(n)
+  else n = Math.floor(n)
   // x mod y = x - n * y
   return arithmetic.sub(x, arithmetic.mul(y, Interval(n)))
 }

diff --git a/test/operations/algebra.js b/test/operations/algebra.js
@@ -40,6 +40,15 @@ describe('algebra', function () {
     assert(Interval.isEmpty(n))
   })
 
+  it('should compute the fmod (issue #15)', function () {
+    // issue #15
+    n = algebra.fmod(
+      new Interval(2, 2),
+      new Interval(2, 2)
+    )
+    Interval.almostEqual(n, [0, 0])
+  })
+
   it('should compute the multiplicative inverse', function () {
     n = algebra.multiplicativeInverse(new Interval(1, 1))
     Interval.almostEqual(n, [1, 1])

diff --git a/test/operations/arithmetic.js b/test/operations/arithmetic.js
@@ -44,6 +44,11 @@ describe('arithmetic', function () {
     )
     assertEps(a.lo, -2)
     assertEps(a.hi, 2)
+    a = arithmetic.sub(
+      new Interval(5, 7),
+      new Interval(2, 3)
+    )
+    Interval.almostEqual(a, [2, 5])
     a = arithmetic.sub(
       new Interval(-1, Infinity),
       new Interval(0, 1)