Micro-optimization in HandleVertexAttribPointer

vertexAttribPointer is a fairly common GL call, so substituting integer
division with bitwise and which has far less latency on common CPU
architectures is a worthwhile optimization.

IsPOT function is added for asserts that make sure this does not break.
Redundant comparison against zero is dropped from IsNPOT. In C++,
unsigned integers are specified to work with mod 2^n arithmetic.

TEST=gpu_unittests
BUG=400135

Review URL: https://codereview.chromium.org/439253002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@287512 0039d316-1c4b-4281-b951-d872f2087c98

gpu/command_buffer/common/gles2_cmd_utils.h

@@ -156,8 +156,14 @@ class GLES2_UTILS_EXPORT GLES2Util {
   static uint32_t GetChannelsNeededForAttachmentType(
       int type, uint32_t max_color_attachments);
 
+  // Return true if value is neither a power of two nor zero.
   static bool IsNPOT(uint32_t value) {
-    return value > 0 && (value & (value - 1)) != 0;
+    return (value & (value - 1)) != 0;
+  }
+
+  // Return true if value is a power of two or zero.
+  static bool IsPOT(uint32_t value) {
+    return (value & (value - 1)) == 0;
   }
 
   static std::string GetStringEnum(uint32_t value);

gpu/command_buffer/service/gles2_cmd_decoder.cc

@@ -7205,13 +7205,15 @@ error::Error GLES2DecoderImpl::HandleVertexAttribPointer(
   }
   GLsizei component_size =
       GLES2Util::GetGLTypeSizeForTexturesAndBuffers(type);
-  if (offset % component_size > 0) {
+  // component_size must be a power of two to use & as optimized modulo.
+  DCHECK(GLES2Util::IsPOT(component_size));
+  if (offset & (component_size - 1)) {
     LOCAL_SET_GL_ERROR(
         GL_INVALID_OPERATION,
         "glVertexAttribPointer", "offset not valid for type");
     return error::kNoError;
   }
-  if (stride % component_size > 0) {
+  if (stride & (component_size - 1)) {
     LOCAL_SET_GL_ERROR(
         GL_INVALID_OPERATION,
         "glVertexAttribPointer", "stride not valid for type");
@@ -7984,8 +7986,7 @@ bool IsValidDXTSize(GLint level, GLsizei size) {
 }
 
 bool IsValidPVRTCSize(GLint level, GLsizei size) {
-  // Ensure that the size is a power of two
-  return (size & (size - 1)) == 0;
+  return GLES2Util::IsPOT(size);
 }
 
 }  // anonymous namespace.