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Eliminate a divide by 40 from the microtime() path on 50Mhz decstatinos 

by approximation using 41/2048. Gains one bit in NTP precision.
This commit is contained in:
jonathan 1999-03-15 09:47:36 +00:00
parent 5965639381
commit c72be5c489
1 changed files with 8 additions and 2 deletions
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10
sys/arch/pmax/pmax/machdep.c
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@ -1,4 +1,4 @@
/* $NetBSD: machdep.c,v 1.125 1999/02/01 00:32:18 nisimura Exp $ */
/* $NetBSD: machdep.c,v 1.126 1999/03/15 09:47:36 jonathan Exp $ */
/*
* Copyright (c) 1988 University of Utah.
@ -43,7 +43,7 @@
#include <sys/cdefs.h> /* RCS ID & Copyright macro defns */
__KERNEL_RCSID(0, "$NetBSD: machdep.c,v 1.125 1999/02/01 00:32:18 nisimura Exp $");
__KERNEL_RCSID(0, "$NetBSD: machdep.c,v 1.126 1999/03/15 09:47:36 jonathan Exp $");
/* from: Utah Hdr: machdep.c 1.63 91/04/24 */
@ -853,7 +853,13 @@ clkread()
extern u_int32_t mips3_cycle_count __P((void));
register u_int32_t mips3_cycles =
mips3_cycle_count() - (u_int32_t)latched_cycle_cnt;
/* XXX divides take 78 cycles: approximate with * 41/2048 */
#if 0
return (mips3_cycles / cpu_mhz);
#else
return((mips3_cycles >> 6) + (mips3_cycles >> 8) +
(mips3_cycles >> 11));
#endif
} else
#endif
#ifdef DEC_MAXINE