Throw RangeError instead of returning NaN (which is not a bigint)

README.md

@@ -148,7 +148,7 @@ iterations of Miller-Rabin Probabilistic Primality Test (FIPS 186-4 C.3.1)</p>
 <dt><a href="#min">min(a, b)</a> ⇒ <code>bigint</code></dt>
 <dd><p>Minimum. min(a,b)==b if a&gt;=b. min(a,b)==a if a&lt;=b</p>
 </dd>
-<dt><a href="#modInv">modInv(a, n)</a> ⇒ <code>bigint</code> | <code>NaN</code></dt>
+<dt><a href="#modInv">modInv(a, n)</a> ⇒ <code>bigint</code></dt>
 <dd><p>Modular inverse.</p>
 </dd>
 <dt><a href="#modPow">modPow(b, e, n)</a> ⇒ <code>bigint</code></dt>
@@ -225,6 +225,10 @@ Take positive integers a, b as input, and return a triple (g, x, y), such that a
 
 **Kind**: global function  
 **Returns**: [<code>egcdReturn</code>](#egcdReturn) - A triple (g, x, y), such that ax + by = g = gcd(a, b).  
+**Throws**:
+
+- <code>RangeError</code> a and b MUST be > 0
+
 
 | Param | Type |
 | --- | --- |
@@ -318,11 +322,15 @@ Minimum. min(a,b)==b if a>=b. min(a,b)==a if a<=b
 
 <a name="modInv"></a>
 
-### modInv(a, n) ⇒ <code>bigint</code> \| <code>NaN</code>
+### modInv(a, n) ⇒ <code>bigint</code>
 Modular inverse.
 
 **Kind**: global function  
-**Returns**: <code>bigint</code> \| <code>NaN</code> - the inverse modulo n or NaN if it does not exist  
+**Returns**: <code>bigint</code> - the inverse modulo n  
+**Throws**:
+
+- <code>RangeError</code> a does not have inverse modulo n
+
 
 | Param | Type | Description |
 | --- | --- | --- |

lib/index.browser.mod.js

@@ -39,6 +39,8 @@ function bitLength (a) {
  * @param {number|bigint} a
  * @param {number|bigint} b
  *
+ * @throws {RangeError} a and b MUST be > 0
+ *
  * @returns {egcdReturn} A triple (g, x, y), such that ax + by = g = gcd(a, b).
  */
 function eGcd (a, b) {
@@ -152,18 +154,16 @@ function min (a, b) {
  * @param {number|bigint} a The number to find an inverse for
  * @param {number|bigint} n The modulo
  *
- * @returns {bigint|NaN} the inverse modulo n or NaN if it does not exist
+ * @throws {RangeError} a does not have inverse modulo n
+ *
+ * @returns {bigint} the inverse modulo n
  */
 function modInv (a, n) {
-  try {
-    const egcd = eGcd(toZn(a, n), n)
-    if (egcd.g !== 1n) {
-      return NaN // modular inverse does not exist
-    } else {
-      return toZn(egcd.x, n)
-    }
-  } catch (error) {
-    return NaN
+  const egcd = eGcd(toZn(a, n), n)
+  if (egcd.g !== 1n) {
+    throw new RangeError(`${a.toString()} does not have inverse modulo ${n.toString()}`) // modular inverse does not exist
+  } else {
+    return toZn(egcd.x, n)
   }
 }
 
@@ -178,7 +178,7 @@ function modInv (a, n) {
  */
 function modPow (b, e, n) {
   n = BigInt(n)
-  if (n === 0n) { return NaN } else if (n === 1n) { return BigInt(0) }
+  if (n === 0n) { throw new RangeError('n must be > 0') } else if (n === 1n) { return BigInt(0) }
 
   b = toZn(b, n)
 

lib/index.node.js

@@ -41,6 +41,8 @@ function bitLength (a) {
  * @param {number|bigint} a
  * @param {number|bigint} b
  *
+ * @throws {RangeError} a and b MUST be > 0
+ *
  * @returns {egcdReturn} A triple (g, x, y), such that ax + by = g = gcd(a, b).
  */
 function eGcd (a, b) {
@@ -154,18 +156,16 @@ function min (a, b) {
  * @param {number|bigint} a The number to find an inverse for
  * @param {number|bigint} n The modulo
  *
- * @returns {bigint|NaN} the inverse modulo n or NaN if it does not exist
+ * @throws {RangeError} a does not have inverse modulo n
+ *
+ * @returns {bigint} the inverse modulo n
  */
 function modInv (a, n) {
-  try {
-    const egcd = eGcd(toZn(a, n), n)
-    if (egcd.g !== 1n) {
-      return NaN // modular inverse does not exist
-    } else {
-      return toZn(egcd.x, n)
-    }
-  } catch (error) {
-    return NaN
+  const egcd = eGcd(toZn(a, n), n)
+  if (egcd.g !== 1n) {
+    throw new RangeError(`${a.toString()} does not have inverse modulo ${n.toString()}`) // modular inverse does not exist
+  } else {
+    return toZn(egcd.x, n)
   }
 }
 
@@ -180,7 +180,7 @@ function modInv (a, n) {
  */
 function modPow (b, e, n) {
   n = BigInt(n)
-  if (n === 0n) { return NaN } else if (n === 1n) { return BigInt(0) }
+  if (n === 0n) { throw new RangeError('n must be > 0') } else if (n === 1n) { return BigInt(0) }
 
   b = toZn(b, n)
 

src/js/bigint-mod-arith.js

@@ -39,6 +39,8 @@ export function bitLength (a) {
  * @param {number|bigint} a
  * @param {number|bigint} b
  *
+ * @throws {RangeError} a and b MUST be > 0
+ *
  * @returns {egcdReturn} A triple (g, x, y), such that ax + by = g = gcd(a, b).
  */
 export function eGcd (a, b) {
@@ -152,18 +154,16 @@ export function min (a, b) {
  * @param {number|bigint} a The number to find an inverse for
  * @param {number|bigint} n The modulo
  *
- * @returns {bigint|NaN} the inverse modulo n or NaN if it does not exist
+ * @throws {RangeError} a does not have inverse modulo n
+ *
+ * @returns {bigint} the inverse modulo n
  */
 export function modInv (a, n) {
-  try {
-    const egcd = eGcd(toZn(a, n), n)
-    if (egcd.g !== 1n) {
-      return NaN // modular inverse does not exist
-    } else {
-      return toZn(egcd.x, n)
-    }
-  } catch (error) {
-    return NaN
+  const egcd = eGcd(toZn(a, n), n)
+  if (egcd.g !== 1n) {
+    throw new RangeError(`${a.toString()} does not have inverse modulo ${n.toString()}`) // modular inverse does not exist
+  } else {
+    return toZn(egcd.x, n)
   }
 }
 
@@ -178,7 +178,7 @@ export function modInv (a, n) {
  */
 export function modPow (b, e, n) {
   n = BigInt(n)
-  if (n === 0n) { return NaN } else if (n === 1n) { return BigInt(0) }
+  if (n === 0n) { throw new RangeError('n must be > 0') } else if (n === 1n) { return BigInt(0) }
 
   b = toZn(b, n)
 

test/modInv.js

@@ -21,21 +21,20 @@ const inputs = [
     a: BigInt(-2),
     n: BigInt(5),
     modInv: BigInt(2)
-  },
+  }]
+
+const invalidInputs = [
   {
     a: BigInt(2),
-    n: BigInt(4),
-    modInv: NaN
+    n: BigInt(4)
   },
   {
     a: BigInt(0),
-    n: BigInt(0),
-    modInv: NaN
+    n: BigInt(0)
   },
   {
     a: BigInt(0),
-    n: BigInt(37),
-    modInv: NaN
+    n: BigInt(37)
   }
 ]
 
@@ -49,4 +48,16 @@ describe('modInv', function () {
       })
     })
   }
+  for (const input of invalidInputs) {
+    describe(`modInv(${input.a}, ${input.n})`, function () {
+      it('should throw RangeError', function () {
+        try {
+          _pkg.modInv(input.a, input.n)
+          throw new Error('should have failed')
+        } catch (err) {
+          chai.expect(err).to.be.instanceOf(RangeError)
+        }
+      })
+    })
+  }
 })

test/modPow.js

@@ -7,12 +7,6 @@ const chai = require('chai')
 // <--
 
 const inputs = [
-  {
-    a: BigInt(4),
-    b: BigInt(-1),
-    n: BigInt(0),
-    modPow: NaN
-  },
   {
     a: BigInt(4),
     b: BigInt(-1),
@@ -42,6 +36,13 @@ const inputs = [
     b: BigInt(3),
     n: BigInt(25),
     modPow: BigInt(2)
+  }]
+
+const invalidInputs = [
+  {
+    a: BigInt(4),
+    b: BigInt(-1),
+    n: BigInt(0)
   }
 ]
 
@@ -55,6 +56,18 @@ describe('modPow', function () {
       })
     })
   }
+  for (const input of invalidInputs) {
+    describe(`modPow(${input.a}, ${input.b}, ${input.n})`, function () {
+      it('should throw RangeError', function () {
+        try {
+          _pkg.modPow(input.a, input.b, input.n)
+          throw new Error('should have failed')
+        } catch (err) {
+          chai.expect(err).to.be.instanceOf(RangeError)
+        }
+      })
+    })
+  }
   describe('Time profiling', function () {
     let iterations = 500
     it(`just testing ${iterations} iterations of a big modular exponentiation (1024 bits)`, function () {

types/index.d.ts

@@ -34,6 +34,8 @@ export function bitLength(a: number | bigint): number;
  * @param {number|bigint} a
  * @param {number|bigint} b
  *
+ * @throws {RangeError} a and b MUST be > 0
+ *
  * @returns {egcdReturn} A triple (g, x, y), such that ax + by = g = gcd(a, b).
  */
 export function eGcd(a: number | bigint, b: number | bigint): egcdReturn;
@@ -91,9 +93,11 @@ export function min(a: number | bigint, b: number | bigint): bigint;
  * @param {number|bigint} a The number to find an inverse for
  * @param {number|bigint} n The modulo
  *
- * @returns {bigint|NaN} the inverse modulo n or NaN if it does not exist
+ * @throws {RangeError} a does not have inverse modulo n
+ *
+ * @returns {bigint} the inverse modulo n
  */
-export function modInv(a: number | bigint, n: number | bigint): number | bigint;
+export function modInv(a: number | bigint, n: number | bigint): bigint;
 /**
  * Modular exponentiation b**e mod n. Currently using the right-to-left binary method
  *