5.3 Program Example

 

• The declaration uses data_t to designate the data type of the underlying elements.
• We allocate the data array block to store the vector elements as an array of len objects of type data_t.

 

 

 

• An important feature to note is that get_vec_element, the vector access routine, performs bounds checking for every vector reference

 

 

 

 

5.4 Eliminating Loop Inefficiencies

 

 

• This optimization is an instance of a general class of optimizations known as code motion
• Figure 5.5 와 Figure 5.6 의 차이는 loop속에 vec_length함수가 들어가서 loop가 돌떄마다 함수를 계속 호출하냐 안하냐 차이
• To improve the code, the programmer must often help the compiler by explicitly performing code motion.

 

 

 

• Function lower2 shown in Figure 5.7 is identical to that of lower1, except that we have moved the call to strlen out of the loop.
• In an ideal world, a compiler would recognize that each call to strlen in the loop test will return the same result, and thus the call could be moved out of the loop.