Fix bigint hex parsing #1945.

lib/std/math/bigint.c3

@@ -92,9 +92,9 @@ fn BigInt*! BigInt.init_string_radix(&self, String value, int radix)
 			case '0'..'9':
 				pos_val -= '0';
 			case 'A'..'Z':
-				pos_val -= 'A' + 10;
+				pos_val -= 'A' - 10;
 			case 'a'..'z':
-				pos_val -= 'a' + 10;
+				pos_val -= 'a' - 10;
 			default:
 				return NumberConversion.MALFORMED_INTEGER?;
 		}

releasenotes.md

@@ -49,6 +49,7 @@
 - Allow function types to have a calling convention. #1938
 - Issue with defer copying when triggered by break or continue #1936.
 - Assert when using optional as init or inc part in a for loop #1942.
+- Fix bigint hex parsing #1945.
 
 ### Stdlib changes
 - Added '%h' and '%H' for printing out binary data in hexadecimal using the formatter.

test/unit/stdlib/math/bigint.c3

@@ -1,5 +1,11 @@
 module std::math::bigint @test;
 
+fn void test_parse16()
+{
+	BigInt bi @noinit;
+    assert(bi.init_string_radix("c", 16)!!.equals(bigint::from_int(12)));
+}
+
 fn void test_plus()
 {
 	BigInt a = bigint::from_int(123);