How do I go about Power and Square root functions in Assembly(IA32)?

Question

How do I go about Power and Square root functions in Assembly Language (with/out) Stack on Linux.

Edit 1 : I'm programming for Intel x_86.

Answer 1

Write a simple few line C program that performs the task you are interested in. Compile that to an object. Disassemble that object....Look at how the assembler prepares to call the math function and how it calls the math function, take the disassembled code segments as your starting point for assembler and go from there.

Now if you are talking some embedded system with no operating system, the problem is not the operating system but the C/math library. Those libraries, in these functions or other, may rely on operating system calls which wont be valid. Ideally though it is the same exact mechanism, prepare for the function call by setting up the right registers, make the call to the function, use the results. With embedded your problem comes when you try to link your code with the library and/or when you try to execute it.

If you are asking how to re-create this functionality without using a pre-made library using discrete instructions. That is a completely different topic, esp if you are using a processor without those instructions. You can learn a little by looking at the source code for the library for those functions, and/or the disassembly of the functions in question, but it is likely not obvious. Look for the book or a book similar to "Hacker's Delight", which is packed full of things like performing math functions that are not natively supported by the language or processor.

Answer 2

In x86 assembly, there is no instruction for a Power operation, but you can build your own routine for calculating Power() by expressing the Power in terms of logarithms.

The following two instructions calculate logarithms:

FYL2X   ; Replace ST(1) with (ST(1) * log2 ST(0)) and pop the register stack.
FYL2XP1 ; Replace ST(1) with (ST(1) * log2(ST(0) + 1.0)) and pop the register stack.

There are several ways to compute the square root:

(1) You can use the FPU instruction

FSQRT ; Computes square root of ST(0) and stores the result in ST(0).

(2) alternatively, you can use the following SSE/SSE2 instructions:

SQRTPD xmm1, xmm2/m128 ;Compute Square Roots of Packed Double-Precision Floating-Point Values
SQRTPS xmm1, xmm2/m128 ;Compute Square Roots of Packed Single-Precision Floating-Point Values
SQRTSS xmm1, xmm2/m128 ;Compute Square Root of Scalar Single-Precision Floating-Point Value
SQRTSD xmm1, xmm2/m128 ;Compute Square Root of Scalar Double-Precision Floating-Point Value