Use mul and div instead of bitshifts to calculate srtt

Use mul and div instead of bitshifts to calculate srtt

There was a microoptimization for smoothing srtt with bitshifts.  Revert
the code to use * 98 / 100, it doesn't really make that difference on
modern CPUs, for comparison here:

    muldiv:
	    imul    eax, edi, 98
	    imul    rax, rax, 1374389535
	    shr     rax, 37
	    ret
    shift:
	    mov     eax, edi
	    sal     eax, 9
	    sub     eax, edi
	    shr     eax, 9
	    ret