optimize IV -> UV conversions

This commit replaces all instances of code that looks like this:

  uv = (iv == IV_MIN) ? (UV)iv : (UV)(-iv)

with simpler and more optimal:

  uv = -(UV)iv

While -iv indeed results in an undefined behaviour when iv == IV_MIN,
-(UV)iv is perfectly well defined and does the right thing.

C standard guarantees that the result of (UV)iv (for negative iv) is
equal to iv + UV_MAX + 1 (see 6.3.1.3, paragraph 2 in C11). It also
guarantees that the result of -uv is UV_MAX - uv + 1 (6.2.5,
paragraph 9).

That means that the result of -(UV)iv is UV_MAX - (iv + UV_MAX + 1) + 1
which is equal to -iv for *all* possible negative values of iv.

[perl #133677]

1 files changed, 2 insertions, 2 deletions

diff --git a/pp_hot.c b/pp_hot.c
index dc02612042..ace5f0208b 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -1521,7 +1521,7 @@ PP(pp_add)
 			auv = aiv;
 			auvok = 1;	/* Now acting as a sign flag.  */
 		    } else {
-			auv = (aiv == IV_MIN) ? (UV)aiv : (UV)(-aiv);
+			auv = -(UV)aiv;
 		    }
 		}
 		a_valid = 1;
@@ -1541,7 +1541,7 @@ PP(pp_add)
 		    buv = biv;
 		    buvok = 1;
 		} else
-                    buv = (biv == IV_MIN) ? (UV)biv : (UV)(-biv);
+                    buv = -(UV)biv;
 	    }
 	    /* ?uvok if value is >= 0. basically, flagged as UV if it's +ve,
 	       else "IV" now, independent of how it came in.