Changeset 87192 in vbox for trunk/src/VBox/Runtime/common

Timestamp:

Jan 7, 2021 8:43:08 PM (4 years ago)

Author:

vboxsync

Message:

iprt/asm.h: Added generic C version of ASMBitFirstClear. Officially specified that the iprt/asm.h bitmaps are little-endian and added missing conversions. bugref:9898

Location:

trunk/src/VBox/Runtime/common/asm

Files:

• ASMBitFirstClear-generic.cpp (copied) (copied from trunk/src/VBox/Runtime/common/asm/ASMMemFirstMismatchingU8-generic.cpp ) (2 diffs)
• asm-fake.cpp (modified) (1 diff)

trunk/src/VBox/Runtime/common/asm/ASMBitFirstClear-generic.cpp

@@ -1 +1 @@
 /* $Id$ */
 /** @file
- * IPRT - ASMMemZeroPage - generic C implementation.
+ * IPRT - ASMBitFirstClear - generic C implementation.
  */
 
@@ -32 +32 @@
 #include "internal/iprt.h"
 
+#include <iprt/assert.h>
 
-DECLASM(void *) ASMMemFirstMismatchingU8(void const RT_FAR *pv, size_t cb, uint8_t u8) RT_NOTHROW_DEF
+
+DECLASM(int32_t) ASMBitFirstClear(const volatile void RT_FAR *pvBitmap, uint32_t cBits) RT_NOTHROW_DEF
 {
-    uint8_t const *pb = (uint8_t const RT_FAR *)pv;
-    for (; cb; cb--, pb++)
-        if (RT_LIKELY(*pb == u8))
-        { /* likely */ }
+    const volatile size_t RT_FAR *pu = (const volatile size_t RT_FAR *)pvBitmap;
+    Assert(!(cBits & 31));
+
+    while (cBits >= sizeof(size_t) * 8)
+    {
+        size_t u = *pu;
+        if (u == ~(size_t)0)
+        { }
         else
-            return (void *)pb;
-    return NULL;
+        {
+            size_t const iBaseBit = ((uintptr_t)pu - (uintptr_t)pvBitmap) * 8;
+#if ARCH_BITS == 32
+            return iBaseBit + ASMBitFirstSetU32(~RT_LE2H_U32(u)) - 1;
+#elif ARCH_BITS == 64
+            return iBaseBit + ASMBitFirstSetU64(~RT_LE2H_U64(u)) - 1;
+#else
+# error "ARCH_BITS or RT_BIG_ENDIAN/RT_LITTLE_ENDIAN is not supported" /** @todo figure out bitmaps on bigendian systems! */
+#endif
+        }
+
+        pu++;
+        cBits -= sizeof(size_t) * 8;
+    }
+
+#if ARCH_BITS > 32
+    if (cBits >= 32)
+    {
+        uint32_t u32 = *(const volatile uint32_t RT_FAR *)pu;
+        if (u32 != UINT32_MAX)
+        {
+            size_t const iBaseBit = ((uintptr_t)pu - (uintptr_t)pvBitmap) * 8;
+            return iBaseBit + ASMBitFirstSetU32(~RT_LE2H_U32(u32)) - 1;
+        }
+    }
+#endif
+
+    return -1;
 }
 

trunk/src/VBox/Runtime/common/asm/asm-fake.cpp

@@ -297 +297 @@
 }
 
-RTDECL(int) ASMBitFirstClear(const volatile void *pvBitmap, uint32_t cBits)
-{
-    uint32_t           iBit = 0;
-    uint8_t volatile *pu8 = (uint8_t volatile *)pvBitmap;
-
-    while (iBit < cBits)
-    {
-        uint8_t u8 = *pu8;
-        if (u8 != UINT8_MAX)
-        {
-            while (u8 & 1)
-            {
-                u8 >>= 1;
-                iBit++;
-            }
-            if (iBit >= cBits)
-                return -1;
-            return iBit;
-        }
-
-        iBit += 8;
-        pu8++;
-    }
-    return -1;
-}
-
 RTDECL(int) ASMBitNextClear(const volatile void *pvBitmap, uint32_t cBits, uint32_t iBitPrev)
 {