what code gcc generates for `x/2` and `x*.5`

.gitignore

*.o

posx.c

/* 
http://stackoverflow.com/questions/895574/what-are-some-good-code-optimization-methods/1354688#1354688

USAGE:

    $ gcc -O3 -msse3 -fomit-frame-pointer -c *.c && objdump -Mintel -S *.o

*/

int posx(unsigned int screen_width, unsigned int window_width) {
  return (screen_width / 2) - (window_width / 2);
}

int posx05(unsigned int screen_width, unsigned int window_width) {
  return (screen_width * 0.5) - (window_width * 0.5);
}

posx.dis

gcc -O3 -msse3 -fomit-frame-pointer -c *.c && objdump -Mintel -S *.o

posx.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <posx>:
   0:	89 f8                	mov    eax,edi
   2:	d1 ee                	shr    esi,1
   4:	d1 e8                	shr    eax,1
   6:	29 f0                	sub    eax,esi
   8:	c3                   	ret    
   9:	eb 05                	jmp    10 <posx05>
   b:	90                   	nop
   c:	90                   	nop
   d:	90                   	nop
   e:	90                   	nop
   f:	90                   	nop

0000000000000010 <posx05>:
  10:	89 ff                	mov    edi,edi
  12:	89 f6                	mov    esi,esi
  14:	f2 48 0f 2a c7       	cvtsi2sd xmm0,rdi
  19:	f2 48 0f 2a ce       	cvtsi2sd xmm1,rsi
  1e:	f2 0f 59 05 00 00 00 	mulsd  xmm0,QWORD PTR [rip+0x0]        # 26 <posx05+0x16>
  25:	00 
  26:	f2 0f 59 0d 00 00 00 	mulsd  xmm1,QWORD PTR [rip+0x0]        # 2e <posx05+0x1e>
  2d:	00 
  2e:	f2 0f 58 c1          	addsd  xmm0,xmm1
  32:	f2 0f 2c c0          	cvttsd2si eax,xmm0
  36:	c3                   	ret