math: add neg? word

Do the right thing with integers or floats

core/math/floats/floats.factor

@@ -74,4 +74,6 @@ M: float prev-float
 
 M: float fp-sign double>bits 63 bit? ; inline
 
+M: float neg? fp-sign ; inline
+
 M: float abs double>bits 63 2^ bitnot bitand bits>double ; inline

core/math/integers/integers.factor

@@ -8,6 +8,8 @@ IN: math.integers.private
 : fixnum-min ( x y -- z ) [ fixnum< ] most ; foldable
 : fixnum-max ( x y -- z ) [ fixnum> ] most ; foldable
 
+M: integer neg? 0 < ; inline
+
 M: integer numerator ; inline
 M: integer denominator drop 1 ; inline
 

core/math/math.factor

@@ -73,6 +73,8 @@ ERROR: log2-expects-positive x ;
 : even? ( n -- ? ) 1 bitand zero? ; inline
 : odd? ( n -- ? ) 1 bitand 1 number= ; inline
 
+GENERIC: neg? ( x -- -x )
+
 : if-zero ( ..a n quot1: ( ..a -- ..b ) quot2: ( ..a n -- ..b ) -- ..b )
     [ dup zero? ] [ [ drop ] prepose ] [ ] tri* if ; inline