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Update to tagged container-libs releases
Signed-off-by: Miloslav Trmač <mitr@redhat.com>
This commit is contained in:
26
vendor/google.golang.org/protobuf/encoding/protowire/wire.go
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26
vendor/google.golang.org/protobuf/encoding/protowire/wire.go
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@@ -371,7 +371,31 @@ func ConsumeVarint(b []byte) (v uint64, n int) {
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func SizeVarint(v uint64) int {
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// This computes 1 + (bits.Len64(v)-1)/7.
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// 9/64 is a good enough approximation of 1/7
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return int(9*uint32(bits.Len64(v))+64) / 64
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//
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// The Go compiler can translate the bits.LeadingZeros64 call into the LZCNT
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// instruction, which is very fast on CPUs from the last few years. The
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// specific way of expressing the calculation matches C++ Protobuf, see
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// https://godbolt.org/z/4P3h53oM4 for the C++ code and how gcc/clang
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// optimize that function for GOAMD64=v1 and GOAMD64=v3 (-march=haswell).
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// By OR'ing v with 1, we guarantee that v is never 0, without changing the
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// result of SizeVarint. LZCNT is not defined for 0, meaning the compiler
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// needs to add extra instructions to handle that case.
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//
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// The Go compiler currently (go1.24.4) does not make use of this knowledge.
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// This opportunity (removing the XOR instruction, which handles the 0 case)
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// results in a small (1%) performance win across CPU architectures.
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//
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// Independently of avoiding the 0 case, we need the v |= 1 line because
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// it allows the Go compiler to eliminate an extra XCHGL barrier.
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v |= 1
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// It would be clearer to write log2value := 63 - uint32(...), but
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// writing uint32(...) ^ 63 is much more efficient (-14% ARM, -20% Intel).
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// Proof of identity for our value range [0..63]:
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// https://go.dev/play/p/Pdn9hEWYakX
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log2value := uint32(bits.LeadingZeros64(v)) ^ 63
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return int((log2value*9 + (64 + 9)) / 64)
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}
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// AppendFixed32 appends v to b as a little-endian uint32.
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