Changeset 44241 in vbox

Timestamp:

Jan 7, 2013 8:17:19 PM (12 years ago)

Author:

vboxsync

svn:sync-xref-src-repo-rev:

83097

Message:

Runtime/sg.cpp: Add API to check a buffer for zeros

Location:

trunk

Files:

• include/iprt/mangling.h (modified) (1 diff)
• include/iprt/sg.h (modified) (1 diff)
• src/VBox/Runtime/common/misc/sg.cpp (modified) (2 diffs)

trunk/include/iprt/mangling.h

@@ -1173 +1173 @@
 # define RTSgBufCopyToBuf                               RT_MANGLER(RTSgBufCopyToBuf)
 # define RTSgBufInit                                    RT_MANGLER(RTSgBufInit)
+# define RTSgBufIsZero                                  RT_MANGLER(RTSgBufIsZero)
 # define RTSgBufReset                                   RT_MANGLER(RTSgBufReset)
 # define RTSgBufSegArrayCreate                          RT_MANGLER(RTSgBufSegArrayCreate)

trunk/include/iprt/sg.h

@@ -220 +220 @@
  */
 RTDECL(size_t) RTSgBufSegArrayCreate(PRTSGBUF pSgBuf, PRTSGSEG paSeg, unsigned *pcSeg, size_t cbData);
+
+/**
+ * Returns whether the given S/G buffer is zeroed out from the current position
+ * upto the number of bytes to check.
+ *
+ * @returns true if the buffer has only zeros
+ *          false otherwise.
+ * @param   pSgBuf      The S/G buffer.
+ * @param   cbCheck     Number of bytes to check.
+ */
+RTDECL(bool) RTSgBufIsZero(PRTSGBUF pSgBuf, size_t cbCheck);
 
 /**

trunk/src/VBox/Runtime/common/misc/sg.cpp

@@ -32 +32 @@
 #include <iprt/string.h>
 #include <iprt/assert.h>
+#include <iprt/asm.h>
 
 
@@ -422 +423 @@
 }
 
+RTDECL(bool) RTSgBufIsZero(PRTSGBUF pSgBuf, size_t cbCheck)
+{
+    bool fIsZero = true;
+    size_t cbLeft = cbCheck;
+    RTSGBUF SgBufTmp;
+
+    RTSgBufClone(&SgBufTmp, pSgBuf);
+
+    while (cbLeft)
+    {
+        size_t cbThisCheck = cbLeft;
+        void *pvBuf = sgBufGet(&SgBufTmp, &cbThisCheck);
+
+        if (!cbThisCheck)
+            break;
+
+        /* Use optimized inline assembler if possible. */
+        if (   !(cbThisCheck % 4)
+            && (cbThisCheck * 8 <= UINT32_MAX))
+        {
+            if (ASMBitFirstSet((volatile void *)pvBuf, cbThisCheck * 8) != -1)
+            {
+                fIsZero = false;
+                break;
+            }
+        }
+        else
+        {
+            for (unsigned i = 0; i < cbThisCheck; i++)
+            {
+                char *pbBuf = (char *)pvBuf;
+                if (*pbBuf)
+                {
+                    fIsZero = false;
+                    break;
+                }
+                pvBuf = pbBuf + 1;
+            }
+
+            if (!fIsZero)
+                break;
+        }
+
+        cbLeft -= cbThisCheck;
+    }
+
+    return fIsZero;
+}
+