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vmx: nanosec: replace the loop with a few div, mod and mul ops

--- a/sys/src/cmd/vmx/nanosec.c

+++ b/sys/src/cmd/vmx/nanosec.c

@@ -2,6 +2,8 @@

 #include <libc.h>

 #include <tos.h>

+#define Nsec 1000000000ULL

+

 /*

  * nsec() is wallclock and can be adjusted by timesync

  * so need to use cycles() instead, but fall back to

@@ -11,7 +13,7 @@

 nanosec(void)

 {

 	static uvlong fasthz, xstart;

-	uvlong x, div;

+	uvlong x;

 	if(fasthz == ~0ULL)

 		return nsec() - xstart;

@@ -18,21 +20,19 @@

 	if(fasthz == 0){

 		if(_tos->cyclefreq){

-			cycles(&xstart);

 			fasthz = _tos->cyclefreq;

+			cycles(&xstart);

 		} else {

-			xstart = nsec();

 			fasthz = ~0ULL;

-			fprint(2, "cyclefreq not available, falling back to nsec()\n");

-			fprint(2, "you might want to disable aux/timesync\n");

-			return 0;

+			xstart = nsec();

 		}

+		return 0;

 	}

 	cycles(&x);

 	x -= xstart;

-	/* this is ugly */

-	for(div = 1000000000ULL; x < 0x1999999999999999ULL && div > 1 ; div /= 10ULL, x *= 10ULL);

+	uvlong q = x / fasthz;

+	uvlong r = x % fasthz;

-	return x / (fasthz / div);

+	return q*Nsec + r*Nsec/fasthz;

 }

-- 

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