diff options
| author | Tom Cosgrove <tom@cvs.openbsd.org> | 2007-06-26 10:53:02 +0000 |
|---|---|---|
| committer | Tom Cosgrove <tom@cvs.openbsd.org> | 2007-06-26 10:53:02 +0000 |
| commit | 4b41f65689d5d92e42d673eed28dda7ac4b3b1cd (patch) | |
| tree | 47e64d16660b28120c0da715e1791633cb808536 /sys/dev/ic/ar5xxx.c | |
| parent | b199d7eb252160b9b683b85377c157a2103ad975 (diff) | |
Implement bit swap for a byte in O(log(N)) rather than O(N), prompted
by an interview question I was asked.
ok reyk@
Diffstat (limited to 'sys/dev/ic/ar5xxx.c')
| -rw-r--r-- | sys/dev/ic/ar5xxx.c | 22 |
1 files changed, 15 insertions, 7 deletions
diff --git a/sys/dev/ic/ar5xxx.c b/sys/dev/ic/ar5xxx.c index 4ba700d3f7c..75d31f4d090 100644 --- a/sys/dev/ic/ar5xxx.c +++ b/sys/dev/ic/ar5xxx.c @@ -1,4 +1,4 @@ -/* $OpenBSD: ar5xxx.c,v 1.41 2007/05/09 16:41:14 reyk Exp $ */ +/* $OpenBSD: ar5xxx.c,v 1.42 2007/06/26 10:53:01 tom Exp $ */ /* * Copyright (c) 2004, 2005, 2006, 2007 Reyk Floeter <reyk@openbsd.org> @@ -626,14 +626,22 @@ ar5k_get_regdomain(struct ath_hal *hal) u_int32_t ar5k_bitswap(u_int32_t val, u_int bits) { - u_int32_t retval = 0, bit, i; + if (bits == 8) { + val = ((val & 0xF0) >> 4) | ((val & 0x0F) << 4); + val = ((val & 0xCC) >> 2) | ((val & 0x33) << 2); + val = ((val & 0xAA) >> 1) | ((val & 0x55) << 1); - for (i = 0; i < bits; i++) { - bit = (val >> i) & 1; - retval = (retval << 1) | bit; - } + return val; + } else { + u_int32_t retval = 0, bit, i; - return (retval); + for (i = 0; i < bits; i++) { + bit = (val >> i) & 1; + retval = (retval << 1) | bit; + } + + return retval; + } } u_int |