util: Add SATURATE macro

Equivalent to clamp(x, 0.0, 1.0) or fsat in NIR. Useful for format
packing, among other uses given the variety of substituions in-tree.

v2: Drop brackets (Eric).

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5100>

src/util/macros.h

@@ -291,6 +291,9 @@ do {                       \
 /** Clamp X to [MIN,MAX].  Turn NaN into MIN, arbitrarily. */
 #define CLAMP( X, MIN, MAX )  ( (X)>(MIN) ? ((X)>(MAX) ? (MAX) : (X)) : (MIN) )
 
+/* Syntax sugar occuring frequently in graphics code */
+#define SATURATE( X ) CLAMP(X, 0.0f, 1.0f)
+
 /** Minimum of two values: */
 #define MIN2( A, B )   ( (A)<(B) ? (A) : (B) )