Learning materials

C Language Features Used in This Course

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This documents summarize the C language features frequently employed in this course.

Compiler

gcc

We choose the gcc C language compiler from GCC (GNU Compiler Collection) as our official compiler. This is the default C compiler on Linux (including the Windows subsystem of Linux, WSL). Use other compilers at your own risk.

Compilation Command

A typical gcc compilation command looks like:

gcc <flags> <arguments>

<flags> are the compilation flags
<arguments> are the source files (.c) and libraries (.o)

Useful Compilation Flags

-O specifies the compilation optimization level
- -O0 reduced optimization, default level, use as baseline
- -O2
- -O3 recommended
- -Ofast with non-standard-compliant optimizations
-I specifies the path to include headers
- No space between -I and the path!
- -I. means to look for headers in the current directory
-l specifies the libraries to use
- -lpthread POSIX thread library
-f specifies flags
- -fpic Position dependent
- -fopenmp enable OpenMP support
-m specifies the architecture
- -march=native use the native architecture
- -m64 use 64-bit architecture
- -msse4.2 use SSE4.2 instruction set
-std specifies the C language standard
- -std=gnu90
- -std=gnu11
- -std=c99 -pedantic
- -std=c11 -pedantic

Performance Optimization in C Language

Compilation optimization
- -O2
- -O3
- -Ofast
- -ffast-math
Selected Optimization Approaches
- Loop unrolling
- Cache awareness
  - Optimize the memory access pattern for better cache performance
  - Loop interchange
  - Loop tiling
- Vectorization (hardware architecture dependent)
  - Intel MMX, SSE, AVX
Memory operations

Block memory operations are usually faster than element-wise operations. The strategy is to use block memory operations whenever possible. The following functions are frequently used in this course:
- Memory allocation/deallocation
  - malloc and free
  - calloc and free
  - aligned_alloc and free (C11)
- Memory block copy/set
  - memcpy
  - memset