Added TBigInt.GetMostSignificantBitIndex and tests

tests/UBigIntTestCases.pas

@@ -70,6 +70,17 @@ type
     procedure TestLongNegative;
   end;
 
+  { TBigIntMostSignificantBitIndexTestCase }
+
+  TBigIntMostSignificantBitIndexTestCase = class(TTestCase)
+  private
+    procedure Test(const ABinValue: string; const AExpectedIndex: Int64);
+  published
+    procedure TestZero;
+    procedure TestShort;
+    procedure TestLong;
+  end;
+
   { TBigIntFromInt64TestCase }
 
   TBigIntFromInt64TestCase = class(TTestCase)
@@ -271,6 +282,37 @@ begin
   Test('-192648F1305DD04757A24C873F29F60B6184B5', -1);
 end;
 
+{ TBigIntMostSignificantBitIndexTestCase }
+
+procedure TBigIntMostSignificantBitIndexTestCase.Test(const ABinValue: string; const AExpectedIndex: Int64);
+var
+  a: TBigInt;
+begin
+  a := TBigInt.FromBinaryString(ABinValue);
+  AssertEquals('BigInt from binary string ''' + ABinValue + ''' did not have its most significant bit at index '''
+    + IntToStr(AExpectedIndex) + '''.',
+    AExpectedIndex, a.GetMostSignificantBitIndex);
+end;
+
+procedure TBigIntMostSignificantBitIndexTestCase.TestZero;
+begin
+  Test('0', -1);
+end;
+
+procedure TBigIntMostSignificantBitIndexTestCase.TestShort;
+begin
+  Test('1', 0);
+  Test('11111101111001', 13);
+  Test('10010111101100001110110101111000', 31);
+end;
+
+procedure TBigIntMostSignificantBitIndexTestCase.TestLong;
+begin
+  Test('111100010101010100011101010100011', 32);
+  Test('11101001101010111101000101010001010101010101111111001010101010010100101000101011111001000111001001100011', 103);
+  Test('111101100011110110111011010111100000000001010111101110101101101100101010110111101011010101001100', 95);
+end;
+
 { TBigIntFromInt64TestCase }
 
 procedure TBigIntFromInt64TestCase.Test(const AValue: Int64);
@@ -903,6 +945,7 @@ end;
 initialization
 
   RegisterTest(TBigIntSignTestCase);
+  RegisterTest(TBigIntMostSignificantBitIndexTestCase);
   RegisterTest(TBigIntFromInt64TestCase);
   RegisterTest(TBigIntFromHexTestCase);
   RegisterTest(TBigIntFromBinTestCase);