Add rygorous's float->srgb8 conversion routine to the stdlib.

Issue #230

docs/ispc.rst

@@ -147,6 +147,7 @@ Contents:
 
     * `Converting Between Array-of-Structures and Structure-of-Arrays Layout`_
     * `Conversions To and From Half-Precision Floats`_
+    * `Converting to sRGB8`_
 
   + `Systems Programming Support`_
 
@@ -3691,6 +3692,22 @@ precise.
     uniform int16 float_to_half_fast(uniform float f)
 
 
+Converting to sRGB8
+-------------------
+
+The sRGB color space is used in many applications in graphics and imaging;
+see the `Wikipedia page on sRGB`_ for more information.  The ``ispc``
+standard library provides two functions for converting floating-point color
+values to 8-bit values in the sRGB space.
+
+.. _Wikipedia page on sRGB: http://en.wikipedia.org/wiki/SRGB
+
+::
+
+    int float_to_srgb8(float v)
+    uniform int float_to_srgb8(uniform float v)
+
+
 Systems Programming Support
 ---------------------------