Fix LE constructor for HEX (#265)

indutny · Feb 24, 2021 · 6196232 · 6196232
1 parent 42a33cb
commit 6196232
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Showing 2 changed files with 68 additions and 51 deletions.
diff --git a/lib/bn.js b/lib/bn.js
@@ -91,23 +91,19 @@
     var start = 0;
     if (number[0] === '-') {
       start++;
-    }
-
-    if (base === 16) {
-      this._parseHex(number, start);
-    } else {
-      this._parseBase(number, base, start);
-    }
-
-    if (number[0] === '-') {
       this.negative = 1;
     }
 
-    this.strip();
-
-    if (endian !== 'le') return;
-
-    this._initArray(this.toArray(), base, endian);
+    if (start < number.length) {
+      if (base === 16) {
+        this._parseHex(number, start, endian);
+      } else {
+        this._parseBase(number, base, start);
+        if (endian === 'le') {
+          this._initArray(this.toArray(), base, endian);
+        }
+      }
+    }
   };
 
   BN.prototype._initNumber = function _initNumber (number, base, endian) {
@@ -183,57 +179,68 @@
     return this.strip();
   };
 
-  function parseHex (str, start, end) {
-    var r = 0;
-    var len = Math.min(str.length, end);
-    for (var i = start; i < len; i++) {
-      var c = str.charCodeAt(i) - 48;
-
-      r <<= 4;
-
-      // 'a' - 'f'
-      if (c >= 49 && c <= 54) {
-        r |= c - 49 + 0xa;
-
-      // 'A' - 'F'
-      } else if (c >= 17 && c <= 22) {
-        r |= c - 17 + 0xa;
+  function parseHex4Bits (string, index) {
+    var c = string.charCodeAt(index);
+    // 'A' - 'F'
+    if (c >= 65 && c <= 70) {
+      return c - 55;
+    // 'a' - 'f'
+    } else if (c >= 97 && c <= 102) {
+      return c - 87;
+    // '0' - '9'
+    } else {
+      return (c - 48) & 0xf;
+    }
+  }
 
-      // '0' - '9'
-      } else {
-        r |= c & 0xf;
-      }
+  function parseHexByte (string, lowerBound, index) {
+    var r = parseHex4Bits(string, index);
+    if (index - 1 >= lowerBound) {
+      r |= parseHex4Bits(string, index - 1) << 4;
     }
     return r;
   }
 
-  BN.prototype._parseHex = function _parseHex (number, start) {
+  BN.prototype._parseHex = function _parseHex (number, start, endian) {
     // Create possibly bigger array to ensure that it fits the number
     this.length = Math.ceil((number.length - start) / 6);
     this.words = new Array(this.length);
     for (var i = 0; i < this.length; i++) {
       this.words[i] = 0;
     }
 
-    var j, w;
-    // Scan 24-bit chunks and add them to the number
+    // 24-bits chunks
     var off = 0;
-    for (i = number.length - 6, j = 0; i >= start; i -= 6) {
-      w = parseHex(number, i, i + 6);
-      this.words[j] |= (w << off) & 0x3ffffff;
-      // NOTE: `0x3fffff` is intentional here, 26bits max shift + 24bit hex limb
-      this.words[j + 1] |= w >>> (26 - off) & 0x3fffff;
-      off += 24;
-      if (off >= 26) {
-        off -= 26;
-        j++;
-      }
-    }
-    if (i + 6 !== start) {
-      w = parseHex(number, start, i + 6);
-      this.words[j] |= (w << off) & 0x3ffffff;
-      this.words[j + 1] |= w >>> (26 - off) & 0x3fffff;
+    var j = 0;
+
+    var w;
+    if (endian === 'be') {
+      for (i = number.length - 1; i >= start; i -= 2) {
+        w = parseHexByte(number, start, i) << off;
+        this.words[j] |= w & 0x3ffffff;
+        if (off >= 18) {
+          off -= 18;
+          j += 1;
+          this.words[j] |= w >>> 26;
+        } else {
+          off += 8;
+        }
+      }
+    } else {
+      var parseLength = number.length - start;
+      for (i = parseLength % 2 === 0 ? start + 1 : start; i < number.length; i += 2) {
+        w = parseHexByte(number, start, i) << off;
+        this.words[j] |= w & 0x3ffffff;
+        if (off >= 18) {
+          off -= 18;
+          j += 1;
+          this.words[j] |= w >>> 26;
+        } else {
+          off += 8;
+        }
+      }
     }
+
     this.strip();
   };
 
@@ -304,6 +311,8 @@
         this._iaddn(word);
       }
     }
+
+    this.strip();
   };
 
   BN.prototype.copy = function copy (dest) {

diff --git a/test/constructor-test.js b/test/constructor-test.js
@@ -90,6 +90,12 @@ describe('BN.js/Constructor', function () {
       assert.equal(new BN('1A6B765D8CDF', 16, 'le').toString(16),
         'df8c5d766b1a');
     });
+
+    it('should accept base-16 LE integer with leading zeros', function () {
+      assert.equal(new BN('0010', 16, 'le').toNumber(), 4096);
+      assert.equal(new BN('-010', 16, 'le').toNumber(), -4096);
+      assert.equal(new BN('010', 16, 'le').toNumber(), 4096);
+    });
   });
 
   describe('with Array input', function () {
@@ -98,6 +104,7 @@ describe('BN.js/Constructor', function () {
     });
 
     it('should import/export big endian', function () {
+      assert.equal(new BN([ 0, 1 ], 16).toString(16), '1');
       assert.equal(new BN([ 1, 2, 3 ]).toString(16), '10203');
       assert.equal(new BN([ 1, 2, 3, 4 ]).toString(16), '1020304');
       assert.equal(new BN([ 1, 2, 3, 4, 5 ]).toString(16), '102030405');
@@ -109,6 +116,7 @@ describe('BN.js/Constructor', function () {
     });
 
     it('should import little endian', function () {
+      assert.equal(new BN([ 0, 1 ], 16, 'le').toString(16), '100');
       assert.equal(new BN([ 1, 2, 3 ], 10, 'le').toString(16), '30201');
       assert.equal(new BN([ 1, 2, 3, 4 ], 10, 'le').toString(16), '4030201');
       assert.equal(new BN([ 1, 2, 3, 4, 5 ], 10, 'le').toString(16),