Efficient clip-testing

Abstract

A method and apparatus for performing fast clip-testing operations in a general purpose processor are provided. This is accomplished by executing a single instruction for comparing a first value x to a second value y and, as a result of the comparison, determining whether x is less than y and whether x-is less than negative y. The values x and y are stored in respective source registers of the processor specified by the instruction. Finally, as a result of the determination, one or more binary values representing the results of the determination are inserted into a destination register of the processor also specified by the instruction. Accordingly, the invention advantageously provides a general purpose processor with the ability to execute a clip-testing function with a single instruction compared with prior art general purpose processors that require multiple instructions to perform the same function. Thus, the general purpose processor of the present invention allows for more efficient and faster clip-testing operations.

1 . A method of performing an instance of a clip instruction that indicates a first value, a second value, a third value, and a destination, the method comprising: 
 comparing the first value against the second value, and    writing to the destination the third value and indications of the comparing.    
   
   
       2 . The method of  claim 1 , wherein the comparing comprises: 
 determining whether the first value is greater than the second value; and    determining whether the first value is less than a negative of the second value.    
   
   
       3 . A sequence of executable instruction instances encoded in one or more machine-readable media, the sequence comprising: 
 an instance of a clip instruction that indicates a first value, a second value, a third value, and a destination register, the clip instruction instance executable to, 
 compare the first value against the second value to determine whether the first value is greater than the second value,  
 compare the first value against a negative of the second value to determine whether the first value is less than the negative of the second value, and  
 write to the destination the third value and indications of the comparisons.  
   
   
   
       4 . An apparatus comprising: 
 at least one processing unit; and    means for performing clip testing with a single instruction instance.