i965: Use bitmask/ffs to iterate used vertex attributes.

Replaces an iterate and test bit in a bitmask loop by a
loop only iterating over the bits set in the bitmask.

v2: Use _mesa_bit_scan{,64} instead of open coding.
v3: Use u_bit_scan{,64} instead of _mesa_bit_scan{,64}.

Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Mathias Fröhlich <Mathias.Froehlich@web.de>

src/mesa/drivers/dri/i965/brw_draw.c

@@ -38,6 +38,7 @@
 #include "swrast/swrast.h"
 #include "swrast_setup/swrast_setup.h"
 #include "drivers/common/meta.h"
+#include "util/bitscan.h"
 
 #include "brw_blorp.h"
 #include "brw_draw.h"
@@ -301,16 +302,15 @@ brw_merge_inputs(struct brw_context *brw,
    }
 
    if (brw->gen < 8 && !brw->is_haswell) {
-      struct gl_program *vp = &ctx->VertexProgram._Current->Base;
+      GLbitfield64 mask = ctx->VertexProgram._Current->Base.InputsRead;
       /* Prior to Haswell, the hardware can't natively support GL_FIXED or
        * 2_10_10_10_REV vertex formats.  Set appropriate workaround flags.
        */
-      for (i = 0; i < VERT_ATTRIB_MAX; i++) {
-         if (!(vp->InputsRead & BITFIELD64_BIT(i)))
-            continue;
-
+      while (mask) {
          uint8_t wa_flags = 0;
 
+         i = u_bit_scan64(&mask);
+
          switch (brw->vb.inputs[i].glarray->Type) {
 
          case GL_FIXED: