When the dividend is known at compile time, we can eliminate some of the
branching and precompute the result for the overflow case.
Before:
B8 54 D3 E6 02 mov eax,2E6D354h
85 FF test edi,edi
74 0C je overflow
3D 00 00 00 80 cmp eax,80000000h
75 0C jne normal_path
83 FF FF cmp edi,0FFFFFFFFh
75 07 jne normal_path
overflow:
C1 F8 1F sar eax,1Fh
8B F8 mov edi,eax
EB 05 jmp done
normal_path:
99 cdq
F7 FF idiv eax,edi
8B F8 mov edi,eax
done:
After:
85 FF test edi,edi
75 04 jne normal_path
33 FF xor edi,edi
EB 0A jmp done
normal_path:
B8 54 D3 E6 02 mov eax,2E6D354h
99 cdq
F7 FF idiv eax,edi
8B F8 mov edi,eax
done:
Fairly common with constant dividend of zero. Non-zero values occur
frequently in Ocarina of Time Master Quest.
Sintendo
c081e3f2b3