util/format: add helper util_format_is_snorm8

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>

src/gallium/auxiliary/util/u_format.c

@@ -169,6 +169,25 @@ util_format_is_snorm(enum pipe_format format)
           desc->channel[i].normalized;
 }
 
+boolean
+util_format_is_snorm8(enum pipe_format format)
+{
+   const struct util_format_description *desc = util_format_description(format);
+   int i;
+
+   if (desc->is_mixed)
+      return FALSE;
+
+   i = util_format_get_first_non_void_channel(format);
+   if (i == -1)
+      return FALSE;
+
+   return desc->channel[i].type == UTIL_FORMAT_TYPE_SIGNED &&
+          !desc->channel[i].pure_integer &&
+          desc->channel[i].normalized &&
+          desc->channel[i].size == 8;
+}
+
 boolean
 util_format_is_luminance_alpha(enum pipe_format format)
 {

src/gallium/auxiliary/util/u_format.h

@@ -686,6 +686,9 @@ util_format_is_pure_uint(enum pipe_format format);
 boolean
 util_format_is_snorm(enum pipe_format format);
 
+boolean
+util_format_is_snorm8(enum pipe_format format);
+
 /**
  * Check if the src format can be blitted to the destination format with
  * a simple memcpy.  For example, blitting from RGBA to RGBx is OK, but not