patch keith-feedback
5291 x86 {high,low}bit rely on undefined behavior

*** 2799,2820 ****
  
  #if defined(__amd64)
  
          ENTRY(lowbit)
          movl    $-1, %eax
!         bsfq    %rdi, %rax
          incl    %eax
          ret
          SET_SIZE(lowbit)
  
  #elif defined(__i386)
  
          ENTRY(lowbit)
-         movl    $-1, %eax
          bsfl    4(%esp), %eax
          incl    %eax
          ret
          SET_SIZE(lowbit)
  
  #endif  /* __i386 */
  #endif  /* __lint */
  
--- 2799,2824 ----
  
  #if defined(__amd64)
  
          ENTRY(lowbit)
          movl    $-1, %eax
!         bsfq    %rdi, %rdi
!         cmovnz  %edi, %eax
          incl    %eax
          ret
          SET_SIZE(lowbit)
  
  #elif defined(__i386)
  
          ENTRY(lowbit)
          bsfl    4(%esp), %eax
+         jz      0f
          incl    %eax
          ret
+ 0:
+         xorl    %eax, %eax
+         ret
          SET_SIZE(lowbit)
  
  #endif  /* __i386 */
  #endif  /* __lint */
  
*** 2823,2886 ****
  /*ARGSUSED*/
  int
  highbit(ulong_t i)
  { return (0); }
  
  #else   /* __lint */
  
  #if defined(__amd64)
  
          ENTRY(highbit)
          movl    $-1, %eax
!         bsrq    %rdi, %rax
          incl    %eax
          ret
          SET_SIZE(highbit)
  
  #elif defined(__i386)
  
          ENTRY(highbit)
-         movl    $-1, %eax
          bsrl    4(%esp), %eax
          incl    %eax
          ret
!         SET_SIZE(highbit)
! 
! #endif  /* __i386 */
! #endif  /* __lint */
! 
! #if defined(__lint)
! 
! /*ARGSUSED*/
! int
! highbit64(uint64_t i)
! { return (0); }
! 
! #else   /* __lint */
! 
! #if defined(__amd64)
! 
!         ENTRY(highbit64)
!         movl    $-1, %eax
!         bsrq    %rdi, %rax
!         incl    %eax
          ret
!         SET_SIZE(highbit64)
! 
! #elif defined(__i386)
  
          ENTRY(highbit64)
          bsrl    8(%esp), %eax
!         jz      .lowbit
!         addl    $32, %eax
!         jmp     .done
! 
! .lowbit:
!         movl    $-1, %eax
!         bsrl    4(%esp), %eax
! .done:
!         incl    %eax
          ret
          SET_SIZE(highbit64)
  
  #endif  /* __i386 */
  #endif  /* __lint */
--- 2827,2871 ----
  /*ARGSUSED*/
  int
  highbit(ulong_t i)
  { return (0); }
  
+ /*ARGSUSED*/
+ int
+ highbit64(uint64_t i)
+ { return (0); }
+ 
  #else   /* __lint */
  
  #if defined(__amd64)
  
          ENTRY(highbit)
+         ALTENTRY(highbit64)
          movl    $-1, %eax
!         bsrq    %rdi, %rdi
!         cmovnz  %edi, %eax
          incl    %eax
          ret
+         SET_SIZE(highbit64)
          SET_SIZE(highbit)
  
  #elif defined(__i386)
  
          ENTRY(highbit)
          bsrl    4(%esp), %eax
+         jz      0f
          incl    %eax
          ret
! 0:
!         xorl    %eax, %eax
          ret    
!         SET_SIZE(highbit)
  
          ENTRY(highbit64)
          bsrl    8(%esp), %eax
!         jz      highbit
!         addl    $33, %eax
          ret
          SET_SIZE(highbit64)
  
  #endif  /* __i386 */
  #endif  /* __lint */