Everyone has CLZ.

Even armv5 had CLZ.

Change-Id: I51bc8d1166d09940fd0d3f4c7717edf26977082c

diff --git a/libc/arch-arm/bionic/ffs.S b/libc/arch-arm/bionic/ffs.S
index c59091f..701af8c 100644 (file)
--- a/libc/arch-arm/bionic/ffs.S
+++ b/libc/arch-arm/bionic/ffs.S
@@ -31,55 +31,11 @@
 #include <machine/asm.h>
 #include <machine/cpu-features.h>
 
-/*
- * ffs - find first set bit, this algorithm isolates the first set
- * bit, then multiplies the number by 0x0450fbaf which leaves the top
- * 6 bits as an index into the table.  This algorithm should be a win
- * over the checking each bit in turn as per the C compiled version.
- *
- * Some newer ARM architectures have an instruction named
- * CLZ (count leading Zero's) that is used
- *
- * This is the ffs algorithm devised by d.seal and posted to comp.sys.arm on
- * 16 Feb 1994.
- */
-
 ENTRY(ffs)
        /* Standard trick to isolate bottom bit in r0 or 0 if r0 = 0 on entry */
        rsb     r1, r0, #0
        ands    r0, r0, r1
-#ifndef __ARM_HAVE_CLZ
-       /*
-        * now r0 has at most one set bit, call this X
-        * if X = 0, all further instructions are skipped
-        */
-       adrne   r2, .L_ffs_table
-       orrne   r0, r0, r0, lsl #4  /* r0 = X * 0x11 */ 
-       orrne   r0, r0, r0, lsl #6  /* r0 = X * 0x451 */
-       rsbne   r0, r0, r0, lsl #16 /* r0 = X * 0x0450fbaf */
-              
-       /* now lookup in table indexed on top 6 bits of r0 */
-       ldrneb  r0, [ r2, r0, lsr #26 ]
-
-       bx              lr
-END(ffs)
-
-.text;
-.type .L_ffs_table, _ASM_TYPE_OBJECT;
-.L_ffs_table:
-/*               0   1   2   3   4   5   6   7           */
-       .byte    0,  1,  2, 13,  3,  7,  0, 14  /*  0- 7 */
-       .byte    4,  0,  8,  0,  0,  0,  0, 15  /*  8-15 */
-       .byte   11,  5,  0,  0,  9,  0,  0, 26  /* 16-23 */
-       .byte    0,  0,  0,  0,  0, 22, 28, 16  /* 24-31 */
-       .byte   32, 12,  6,  0,  0,  0,  0,  0  /* 32-39 */
-       .byte   10,  0,  0, 25,  0,  0, 21, 27  /* 40-47 */
-       .byte   31,  0,  0,  0,  0, 24,  0, 20  /* 48-55 */
-       .byte   30,  0, 23, 19, 29, 18, 17,  0  /* 56-63 */
-#else /* !defined(__ARM_HAVE_CLZ) */
        clzne   r0, r0
        rsbne   r0, r0, #32
        bx              lr
 END(ffs)
-#endif /* !defined(__ARM_HAVE_CLZ) */
-

diff --git a/tests/Android.mk b/tests/Android.mk
index eb97e6c..da9d676 100644 (file)
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -71,6 +71,7 @@ test_src_files = \
     stdio_test.cpp \
     stdlib_test.cpp \
     string_test.cpp \
+    strings_test.cpp \
     stubs_test.cpp \
     unistd_test.cpp \
 

diff --git a/tests/strings_test.cpp b/tests/strings_test.cpp
new file mode 100644 (file)
index 0000000..5200859
--- /dev/null
+++ b/tests/strings_test.cpp
@@ -0,0 +1,32 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+
+#include <errno.h>
+#include <strings.h>
+
+TEST(strings, ffs) {
+  ASSERT_EQ( 0, ffs(0x00000000));
+  ASSERT_EQ( 1, ffs(0x00000001));
+  ASSERT_EQ( 6, ffs(0x00000020));
+  ASSERT_EQ(11, ffs(0x00000400));
+  ASSERT_EQ(16, ffs(0x00008000));
+  ASSERT_EQ(17, ffs(0x00010000));
+  ASSERT_EQ(22, ffs(0x00200000));
+  ASSERT_EQ(27, ffs(0x04000000));
+  ASSERT_EQ(32, ffs(0x80000000));
+}