github.com/afumu/libc@v0.0.6/musl/src/math/i386/atan.s (about)

     1  .global atan
     2  .type atan,@function
     3  atan:
     4  	fldl 4(%esp)
     5  	mov 8(%esp),%eax
     6  	add %eax,%eax
     7  	cmp $0x00200000,%eax
     8  	jb 1f
     9  	fld1
    10  	fpatan
    11  	fstpl 4(%esp)
    12  	fldl 4(%esp)
    13  	ret
    14  		# subnormal x, return x with underflow
    15  1:	fsts 4(%esp)
    16  	ret