log (sm4 - asm)

Component-wise log base 2.

log[_sat] dest[.mask], [-]src0[_abs][.swizzle
Item Description
[in] The address of the result of the operation.
dest = log2(src0)
[in] The value for the operation.



  • Follows limit theory.
  • Error tolerance: If src0 is [0.5..2], absolue error must be no more than 2-21. If src0 is (0..0.5) or (2..+INF], relative error must be no more than 2-21.

The following table shows the results obtained when executing the instruction with various classes of numbers, assuming that neither overflow or underflow occurs. F means finite-real number.

src -inf -F -denorm -0 +0 +denorm +F +inf NaN
dest NaN NaN -inf -inf -inf -inf F +inf NaN

This instruction applies to the following shader stages:

Vertex Shader Geometry Shader Pixel Shader
x x x

Minimum Shader Model

This function is supported in the following shader models.

Shader Model Supported
Shader Model 5 yes
Shader Model 4.1 yes
Shader Model 4 yes
Shader Model 3 (DirectX HLSL) no
Shader Model 2 (DirectX HLSL) no
Shader Model 1 (DirectX HLSL) no

Shader Model 4 Assembly (DirectX HLSL)