[MERGE #5662 @duongnhn] add nativetest for FInitFromDigits method of unsigned BigInt class

Merge pull request #5662 from duongnhn:user/duongn/nativetest-unsigned-bigint

method: initialize an unsigned BigInt from char of decimal digits.

Author: duongnhn

bin/NativeTests/BigIntTest.cpp

@@ -222,4 +222,54 @@ namespace BigIntTest
         {
         }
     }
+
+    TEST_CASE("Init_From_Char_Of_Digits", "[BigIntTest]")
+    {
+        BigInt biDec;
+        char *charDigit;
+        bool result;
+        int charDigitLength;
+
+        SECTION("2**32-1 should have length = 1")
+        {
+            charDigit = "4294967295";
+            charDigitLength = 10;
+            result = biDec.FInitFromDigits(charDigit, charDigitLength, &charDigitLength);
+            REQUIRE(result);
+            int length = biDec.Clu();
+            CHECK(length == 1);
+            uint32 digit = biDec.Lu(0);
+            CHECK(digit == 4294967295);
+        }
+
+        SECTION("2**32+2 should have length = 2")
+        {
+            charDigit = "4294967298";
+            charDigitLength = 10;
+            result = biDec.FInitFromDigits(charDigit, charDigitLength, &charDigitLength);
+            REQUIRE(result);
+            int length = biDec.Clu();
+            CHECK(length == 2);
+            uint32 digit = biDec.Lu(0);
+            CHECK(digit == 2);
+            digit = biDec.Lu(1);
+            CHECK(digit == 1);
+        }
+        
+        SECTION("2**64 should have length = 3")
+        {
+            charDigit = "18446744073709551616";
+            charDigitLength = 20;
+            result = biDec.FInitFromDigits(charDigit, charDigitLength, &charDigitLength);
+            REQUIRE(result);
+            int length = biDec.Clu();
+            CHECK(length == 3);
+            uint32 digit = biDec.Lu(0);
+            CHECK(digit == 0);
+            digit = biDec.Lu(1);
+            CHECK(digit == 0);
+            digit = biDec.Lu(2);
+            CHECK(digit == 1);
+        }
+    }
 }

lib/Common/DataStructures/BigInt.h

@@ -40,7 +40,7 @@ namespace Js
         bool FInitFromRglu(uint32 *prglu, int32 clu); // init from array and length
         bool FInitFromBigint(BigInt *pbiSrc); 
         template <typename EncodedChar>
-        bool FInitFromDigits(const EncodedChar *prgch, int32 cch, int32 *pcchDec); 
+        bool FInitFromDigits(const EncodedChar *prgch, int32 cch, int32 *pcchDec); // init from char of digits
         bool FMulAdd(uint32 luMul, uint32 luAdd);
         bool FMulPow5(int32 c5);
         bool FShiftLeft(int32 cbit);