Merge pull request #177 from steve-h/randomwork

Implement random function to be similar to Python random.uniform()
davedelong · Aug 28, 2020 · 6f5bd12 · 6f5bd12
2 parents 3342c56 + 6c8a9fb
commit 6f5bd12
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Showing 2 changed files with 39 additions and 4 deletions.
diff --git a/MathParser/Sources/MathParser/Functions+Defaults.swift b/MathParser/Sources/MathParser/Functions+Defaults.swift
@@ -179,15 +179,23 @@ extension Function {
             let argValue = try state.evaluator.evaluate(arg, substitutions: state.substitutions)
             argValues.append(argValue)
         }
-
+        var lowerBound = 0.0
-        let lowerBound = argValues.count > 0 ? argValues[0] : Double.leastNormalMagnitude
+        var upperBound = 1.0
-        let upperBound = argValues.count > 1 ? argValues[1] : Double.greatestFiniteMagnitude
+        switch argValues.count {
+        case 1:
+            upperBound = argValues[0]
+        case 2:
+            lowerBound = argValues[0]
+            upperBound = argValues[1]
+        default:
+            break
+        }
 
         guard lowerBound < upperBound else { throw MathParserError(kind: .invalidArguments, range: state.expressionRange) }
 
         let range = upperBound - lowerBound
 
-        return (drand48().truncatingRemainder(dividingBy: range)) + lowerBound
+        return drand48() * range + lowerBound
     })
 
     public static let log = Function(name: "log", evaluator: { state throws -> Double in

diff --git a/MathParser/Tests/MathParserTests/GithubIssues.swift b/MathParser/Tests/MathParserTests/GithubIssues.swift
@@ -377,4 +377,31 @@ class GithubIssues: XCTestCase {
         guard let d2 = XCTAssertNoThrows(try "-2++3".evaluate()) else { return }
         XCTAssertEqual(d2, 1)
     }
+
+    func testIssue158() {
+        srand48(282828)
+        guard let d1 = XCTAssertNoThrows(try "random()".evaluate()) else { return }
+        XCTAssertLessThanOrEqual(d1, 0.4662)
+        XCTAssertGreaterThanOrEqual(0.4661, d1)
+
+        srand48(298298)
+        guard let d2 = XCTAssertNoThrows(try "random(100)".evaluate()) else { return }
+        XCTAssertLessThanOrEqual(d2, 75.79)
+        XCTAssertLessThanOrEqual(75.78, d2)
+
+        srand48(828282)
+        var total: Double = 0.0
+        for _ in 1..<10 {
+            guard let d3 = XCTAssertNoThrows(try "random(100,600)".evaluate()) else { return }
+            total += d3
+        }
+        XCTAssertGreaterThanOrEqual(total / 10, 270)
+        XCTAssertLessThanOrEqual(total / 10, 271)
+
+        srand48(400400)
+        guard let d4 = XCTAssertNoThrows(try "random(-10.0, 10.0)".evaluate()) else { return }
+        XCTAssertLessThanOrEqual(d4, -1.69)
+        XCTAssertLessThanOrEqual( -1.70, d4)
+
+    }
 }