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On 27/07/17 14:27, Corinna Vinschen wrote:
On Jul 27 13:24, Sebastian Huber wrote:On 27/07/17 13:13, Eric Blake wrote:On 07/27/2017 03:06 AM, Sebastian Huber wrote:Signed-off-by: Sebastian Huber<sebastian.huber@embedded-brains.de> --- newlib/libc/misc/ffs.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/newlib/libc/misc/ffs.c b/newlib/libc/misc/ffs.c index ba5700920..a09cbd3bb 100644 --- a/newlib/libc/misc/ffs.c +++ b/newlib/libc/misc/ffs.c @@ -31,6 +31,17 @@ No supporting OS subroutines are required. */ int ffs(int i) { +#ifdef __LP64__ + /* GCC would expand the __builtin_ffs() to ffs() in this case */ + int bit; + + if (i == 0) + return (0); + for (bit = 1; !(i & 1); bit++) + i = (unsigned int)i >> 1; + return (bit);If we're going to open-code it to work around the compiler creating an infloop recursion to ffs(), at least code a straight-line version without branches, rather than the painfully slow bit-by-bit loop. There's plenty of examples on the web of writing ffs() by using bit-twiddling without branching.This is roughly the same implementation we had before. I do not intend to optimize this.Still, __LP64__ is unacceptable. Cygwin would be affected by this as well and would have to revert to its former own ffs implementation. Reverting to a C-based implementation should only be performed on a case-by-case basis.
Yes, so maybe something like this #if defined(__LP64__) && defined(__riscv) or a target-specific ffs.c file similar to memcpy.c, etc. -- Sebastian Huber, embedded brains GmbH Address : Dornierstr. 4, D-82178 Puchheim, Germany Phone : +49 89 189 47 41-16 Fax : +49 89 189 47 41-09 E-Mail : sebastian.huber@embedded-brains.de PGP : Public key available on request. Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
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