log - ps

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

Pixel shader versions	1_1	1_2	1_3	1_4	2_0	2_x	2_sw	3_0	3_sw
log					x	x	x	x	x

The following code snippet 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.