Minor tweaks to memset

git-svn-id: http://svn.code.sf.net/p/nuttx/code/trunk@5245 42af7a65-404d-4744-a932-0658087f49c3

nuttx/Documentation/NuttxPortingGuide.html

@@ -4452,6 +4452,7 @@ build
 <ul><li>
   <code>CONFIG_MEMCPY_VIK</code>:
   Select this option to use the optimized <code>memcpy()</code> function by Daniel Vik.
+  Select this option for improved performance at the expense of increased size. 
   See licensing information in the top-level <code>COPYING</code> file.
   Default: <code>n</code>.
 </li></ul>

nuttx/configs/README.txt

@@ -625,8 +625,9 @@ defconfig -- This is a configuration file similar to the Linux
   Vik's optimized implementation of memcpy():
 
     CONFIG_MEMCPY_VIK - Select this option to use the optimized memcpy()
-      function by Daniel Vik.  See licensing information in the top-level
+      function by Daniel Vik.  Select this option for improved performance
-      COPYING file.  Default: n
+      at the expense of increased size. See licensing information in the
+      top-level COPYING file.  Default: n
 
   And if CONFIG_MEMCPY_VIK is selected, the following tuning options are available:
 
@@ -636,7 +637,8 @@ defconfig -- This is a configuration file similar to the Linux
     CONFIG_MEMCPY_INDEXED_COPY - Copying data using array indexing. Using
       this option, disables the CONFIG_MEMCPY_PRE_INC_PTRS option.
 
-    CONFIG_MEMCPY_64BIT - Compiles memcpy for 64 bit architectures
+    CONFIG_MEMCPY_64BIT - Compiles memcpy for architectures that suppport
+      64-bit operations efficiently.
 
   If CONFIG_ARCH_MEMSET is not selected, then the following option is
   also available:
@@ -647,7 +649,8 @@ defconfig -- This is a configuration file similar to the Linux
   And if CONFIG_MEMSET_OPTSPEED is selected, the following tuning option is
   available:
 
-    CONFIG_MEMSET_64BIT - Compiles memset() for 64 bit architectures
+    CONFIG_MEMSET_64BIT - Compiles memset() for architectures that suppport
+      64-bit operations efficiently.
 
   The architecture may provide custom versions of certain standard header
   files:

nuttx/lib/Kconfig

@@ -165,8 +165,8 @@ config MEMCPY_VIK
 	depends on !ARCH_MEMCPY
 	---help---
 		Select this option to use the optimized memcpy() function by Daniel Vik.
-		Select this option to option for speed at the expense of increased size.
+		Select this option for improved performance at the expense of increased
-		See licensing information in the top-level COPYING file.
+		size. See licensing information in the top-level COPYING file.
 
 if MEMCPY_VIK
 config MEMCPY_PRE_INC_PTRS
@@ -186,7 +186,8 @@ config MEMCPY_64BIT
 	bool "64-bit memcpy()"
 	default n
 	---help---
-		Compiles memcpy() for 64 bit architectures
+		Compiles memcpy() for architectures that suppport 64-bit operations
+		efficiently.
 
 endif
 
@@ -224,7 +225,8 @@ config MEMSET_64BIT
 	default n
 	depends on MEMSET_OPTSPEED
 	---help---
-		Compiles memset() for 64 bit architectures
+		Compiles memset() for architectures that suppport 64-bit operations
+		efficiently.
 
 config ARCH_STRCMP
 	bool "strcmp()"

nuttx/lib/string/lib_memset.c

@@ -92,7 +92,7 @@ void *memset(void *s, int c, size_t n)
           n    -= 1;
         }
 
-      /* Check if there are at least 16-bits left to be zeroed */
+      /* Check if there are at least 16-bits left to be written */
 
       if (n >= 2)
         {
@@ -108,7 +108,7 @@ void *memset(void *s, int c, size_t n)
             }
 
 #ifndef CONFIG_MEMSET_64BIT
-          /* Loop while there are at least 32-bits left to be zeroed */
+          /* Loop while there are at least 32-bits left to be written */
 
           while (n >= 4)
             {
@@ -117,7 +117,7 @@ void *memset(void *s, int c, size_t n)
               n    -= 4;
             }
 #else
-          /* Check if there are at least 32-bits left to be zeroed */
+          /* Check if there are at least 32-bits left to be written */
 
           if (n >= 4)
             {
@@ -132,7 +132,7 @@ void *memset(void *s, int c, size_t n)
                   n    -= 4;
                 }
 
-              /* Loop while there are at least 64-bits left to be zeroed */
+              /* Loop while there are at least 64-bits left to be written */
 
               while (n >= 8)
                 {
@@ -145,16 +145,16 @@ void *memset(void *s, int c, size_t n)
         }
 
 #ifdef CONFIG_MEMSET_64BIT
-    /* We may get here with n in the range 0..7.  If n >= 4, then we should
+      /* We may get here with n in the range 0..7.  If n >= 4, then we should
-     * have 64-bit alignment.
+       * have 64-bit alignment.
-     */
+       */
 
-    if (n >= 4)
+      if (n >= 4)
-      {
+        {
-        *(uint32_t*)addr = val32;
+          *(uint32_t*)addr = val32;
-        addr += 4;
+          addr += 4;
-        n    -= 4;
+          n    -= 4;
-      }
+        }
 #endif
 
       /* We may get here under the following conditions:
@@ -165,23 +165,16 @@ void *memset(void *s, int c, size_t n)
        *   n = 3, addr is aligned to a 32-bit boundary
        */
 
-      switch (n)
+      if (n >= 2)
         {
-          default:
+          *(uint16_t*)addr = val16;
-          case 0:
+          addr += 2;
-            DEBUGASSERT(n == 0);
+          n    -= 2;
-            break;
+        }
 
-          case 2:
+      if (n >= 1)
-            *(uint16_t*)addr = val16;
+        {
-            break;
+          *(uint8_t*)addr = (uint8_t)c;
-
-          case 3:
-            *(uint16_t*)addr = val16;
-            addr += 2;
-          case 1:
-            *(uint8_t*)addr = (uint8_t)c;
-            break;
         }
     }
 #else