Changeset 58758 in vbox

Timestamp:

Nov 19, 2015 1:00:30 AM (9 years ago)

Author:

vboxsync

Message:

IPRT: Implemented ASMBitNextClear in assembly.

Location:

trunk/src/VBox/Runtime

Files:

• Makefile.kmk (modified) (1 diff)
• common/asm/ASMBitNextClear.asm (copied) (copied from trunk/src/VBox/Runtime/common/asm/ASMBitNextSet.asm ) (7 diffs)

trunk/src/VBox/Runtime/Makefile.kmk

@@ -182 +182 @@
         common/asm/ASMBitFirstClear.asm \
         common/asm/ASMBitFirstSet.asm \
+        common/asm/ASMBitNextClear.asm \
         common/asm/ASMBitNextSet.asm \
         common/asm/ASMMultU32ByU32DivByU32.asm \

trunk/src/VBox/Runtime/common/asm/ASMBitNextClear.asm

@@ -1 +1 @@
 ; $Id$
 ;; @file
-; IPRT - ASMBitNextSet().
+; IPRT - ASMBitNextClear().
 ;
 
@@ -34 +34 @@
 
 ;;
-; Finds the first set bit in a bitmap.
+; Finds the first clear bit in a bitmap.
 ;
 ; @returns (32/64:eax, 16:ax+dx)   Index of the first zero bit.
-; @returns (32/64:eax, 16:ax+dx)  -1 if no set bit was found.
+; @returns (32/64:eax, 16:ax+dx)  -1 if no clear bit was found.
 ; @param   msc:rcx gcc:rdi pvBitmap    Pointer to the bitmap.
 ; @param   msc:edx gcc:rsi cBits       The number of bits in the bitmap. Multiple of 32.
@@ -45 +45 @@
 ;          it started out with the ASMBit* API, so that's why we still have it.
 ;
-BEGINPROC_EXPORTED ASMBitNextSet
+BEGINPROC_EXPORTED ASMBitNextClear
 %if ARCH_BITS == 16
         push    bp
@@ -86 +86 @@
 
 %if ARCH_BITS == 16
-        mov     edx, [es:di]            ; edx = current dword
+        mov     edx, [es:di]
 %else
-        mov     edx, [xDI]              ; edx = current dword
+        mov     edx, [xDI]
 %endif
+        not     edx                     ; edx = inverted current dword
         shr     edx, cl                 ; Shift out bits that we have searched.
         jz      .next_dword             ; If zero, nothing to find. Go rep scasd.
         shl     edx, cl                 ; Shift it back so bsf will return the right index.
 
-        bsf     edx, edx                ; edx=index of first set bit
+        bsf     edx, edx                ; edx=index of first clear bit
 
         shl     eax, 3                  ; Turn eax back into a bit offset of the current dword.
@@ -139 +140 @@
 
         ; Do the scanning.
-        xor     eax, eax
+        mov     eax, 0ffffffffh
         repe scasd
         je      .return_failure
@@ -147 +148 @@
 %if ARCH_BITS == 16
         movzx   edi, di
-        mov     eax, [es:xDI]
+        xor     eax, [es:xDI]
 %else
-        mov     eax, [xDI]
+        xor     eax, [xDI]
 %endif
         bsf     eax, eax
@@ -170 +171 @@
         mov     eax, 0ffffffffh
         jmp     .return
-ENDPROC ASMBitNextSet
+ENDPROC ASMBitNextClear