check if fixed point square root in renderer can be replaced with hardware squareroot instruction

[Kuratius]

https://github.com/Hydr8gon/sm64/blob/nds/src/nds/nds_renderer.c

[Kuratius]

https://github.com/devkitPro/libnds/blob/b37c88de856b8e0e8d4ea99b54c7f27b0ed5ec40/include/nds/arm9/math.h#L226

Seems to have implementations in the header file

[Hydr8gon]

For some reason, I didn't think fixed-point square root could be done by shifting a regular square root. You're right; this can be replaced with the hardware function.

[Kuratius]

Do the 64bit and 32 bit squareroots have identical performance for the hardware instruction? I can't tell without checking what the compiler generates in terms of load/store instructions and prologue. I don't expect the nds to have 64 bit registers, but I didn't really check.
Depending on the range of an int on an nds a 32 bit value may be enough even with shifting it. For example squareroot of a 64 bit int can never Take more than 32 bits if it is again an integer and not a float.

[Kuratius]

if (s > 0)

I think this will always evaluate to true except for NaN and s=0

since s is the squared norm of a vector. Does either of these happen?

Does the compiler recognize this?

[Hydr8gon]

According to GBATEK, execution time is the same for both square root modes. The greater than zero check is just a precaution to avoid dividing by zero. Either way, we're talking about micro-optimizations that won't have any measurable impact on performance.