# Introduction

For test purposes, environment variables can be set to control libyuv behavior.  These should only be used for testing, to narrow down bugs or to test performance.

# CPU

By default the cpu is detected and the most advanced form of SIMD is used.  But you can disable instruction sets selectively, or completely, falling back on C code.  Set the variable to 1 to disable the specified instruction set.

## All CPUs
    LIBYUV_DISABLE_ASM

## Intel CPUs
    LIBYUV_DISABLE_X86
    LIBYUV_DISABLE_SSE2
    LIBYUV_DISABLE_SSSE3
    LIBYUV_DISABLE_SSE41
    LIBYUV_DISABLE_SSE42
    LIBYUV_DISABLE_AVX
    LIBYUV_DISABLE_AVX2
    LIBYUV_DISABLE_ERMS
    LIBYUV_DISABLE_FMA3
    LIBYUV_DISABLE_F16C
    LIBYUV_DISABLE_AVX512BW
    LIBYUV_DISABLE_AVX512VL
    LIBYUV_DISABLE_AVX512VBMI
    LIBYUV_DISABLE_AVX512VBMI2
    LIBYUV_DISABLE_AVX512VBITALG
    LIBYUV_DISABLE_AVX512VPOPCNTDQ
    LIBYUV_DISABLE_GFNI

## ARM CPUs

    LIBYUV_DISABLE_NEON

## MIPS CPUs
    LIBYUV_DISABLE_MSA
    LIBYUV_DISABLE_MMI

# Test Width/Height/Repeat

The unittests default to a small image (128x72) to run fast.  This can be set by environment variable to test a specific resolutions.
You can also repeat the test a specified number of iterations, allowing benchmarking and profiling.

    set LIBYUV_WIDTH=1280
    set LIBYUV_HEIGHT=720
    set LIBYUV_REPEAT=999
    set LIBYUV_FLAGS=-1
    set LIBYUV_CPU_INFO=-1