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log - vs

  • Article

Full precision log₂(x).

Syntax

log dst, src

 

where

  • dst is the destination register.
  • src is a source register. Source register requires explicit use of replicate swizzle, that is, exactly one of the .x, .y, .z, .w swizzle components (or the .r, .g, .b, .a equivalents) must be specified.

Remarks

Vertex shader versions 1_1 2_0 2_x 2_sw 3_0 3_sw
log x x x x x x

 

The following code fragment shows the operations performed.

float v = abs(src);
if (v != 0)
{
    dest.x = dest.y = dest.z = dest.w = 
        (float)(log(v)/log(2));  
}
else
{
    dest.x = dest.y = dest.z = dest.w = -FLT_MAX;
}

This instruction accepts a scalar source whose sign bit is ignored. The result is replicated to all four channels.

This instruction provides 21 bits of precision.

Vertex Shader Instructions