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authorDavid Howells <dhowells@redhat.com>2006-12-08 05:37:49 -0500
committerLinus Torvalds <torvalds@woody.osdl.org>2006-12-08 11:28:51 -0500
commitf0d1b0b30d250a07627ad8b9fbbb5c7cc08422e8 (patch)
tree0aa5379150574374351fb92af7881a48dbfcf2ce /include/asm-frv/bitops.h
parentb3d7ae5f47a58a9f7b152deeaf7daa1fc558a8f1 (diff)
[PATCH] LOG2: Implement a general integer log2 facility in the kernel
This facility provides three entry points: ilog2() Log base 2 of unsigned long ilog2_u32() Log base 2 of u32 ilog2_u64() Log base 2 of u64 These facilities can either be used inside functions on dynamic data: int do_something(long q) { ...; y = ilog2(x) ...; } Or can be used to statically initialise global variables with constant values: unsigned n = ilog2(27); When performing static initialisation, the compiler will report "error: initializer element is not constant" if asked to take a log of zero or of something not reducible to a constant. They treat negative numbers as unsigned. When not dealing with a constant, they fall back to using fls() which permits them to use arch-specific log calculation instructions - such as BSR on x86/x86_64 or SCAN on FRV - if available. [akpm@osdl.org: MMC fix] Signed-off-by: David Howells <dhowells@redhat.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: David Howells <dhowells@redhat.com> Cc: Wojtek Kaniewski <wojtekka@toxygen.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'include/asm-frv/bitops.h')
-rw-r--r--include/asm-frv/bitops.h44
1 files changed, 44 insertions, 0 deletions
diff --git a/include/asm-frv/bitops.h b/include/asm-frv/bitops.h
index 1f70d47148bd..f8560edf59ff 100644
--- a/include/asm-frv/bitops.h
+++ b/include/asm-frv/bitops.h
@@ -256,6 +256,50 @@ int __ffs(unsigned long x)
256 return 31 - bit; 256 return 31 - bit;
257} 257}
258 258
259/*
260 * special slimline version of fls() for calculating ilog2_u32()
261 * - note: no protection against n == 0
262 */
263#define ARCH_HAS_ILOG2_U32
264static inline __attribute__((const))
265int __ilog2_u32(u32 n)
266{
267 int bit;
268 asm("scan %1,gr0,%0" : "=r"(bit) : "r"(n));
269 return 31 - bit;
270}
271
272/*
273 * special slimline version of fls64() for calculating ilog2_u64()
274 * - note: no protection against n == 0
275 */
276#define ARCH_HAS_ILOG2_U64
277static inline __attribute__((const))
278int __ilog2_u64(u64 n)
279{
280 union {
281 u64 ll;
282 struct { u32 h, l; };
283 } _;
284 int bit, x, y;
285
286 _.ll = n;
287
288 asm(" subcc %3,gr0,gr0,icc0 \n"
289 " ckeq icc0,cc4 \n"
290 " cscan.p %3,gr0,%0 ,cc4,0 \n"
291 " setlos #63,%1 \n"
292 " cscan.p %4,gr0,%0 ,cc4,1 \n"
293 " setlos #31,%2 \n"
294 " csub.p %1,%0,%0 ,cc4,0 \n"
295 " csub %2,%0,%0 ,cc4,1 \n"
296 : "=&r"(bit), "=r"(x), "=r"(y)
297 : "0r"(_.h), "r"(_.l)
298 : "icc0", "cc4"
299 );
300 return bit;
301}
302
259#include <asm-generic/bitops/sched.h> 303#include <asm-generic/bitops/sched.h>
260#include <asm-generic/bitops/hweight.h> 304#include <asm-generic/bitops/hweight.h>
261 305