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Use mul and div instead of bitshifts to calculate srtt

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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
This commit is contained in:
Ondřej Surý 2023-10-12 09:20:42 +02:00
parent 0635bd01cb
commit 91f3b0edee
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GPG key ID: 2820F37E873DEA41
1 changed files with 2 additions and 4 deletions
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6
lib/dns/adb.c
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@ -3052,10 +3052,8 @@ adjustsrtt(dns_adbaddrinfo_t *addr, unsigned int rtt, unsigned int factor,
if (factor == DNS_ADB_RTTADJAGE) {
if (atomic_load(&addr->entry->lastage) != now) {
new_srtt = addr->entry->srtt;
new_srtt <<= 9;
new_srtt -= addr->entry->srtt;
new_srtt >>= 9;
new_srtt = (uint64_t)atomic_load(&addr->entry->srtt) *
98 / 100;
atomic_store(&addr->entry->lastage, now);
atomic_store(&addr->entry->srtt, new_srtt);
addr->srtt = new_srtt;