Re: [Libguestfs] [PATCH libnbd] generator/Go.ml: Simplify copy_uint32_array

Create a slice backed up by the entries pointer, and copy the data with builtin copy(). This can be 3x times faster but I did not measure it. Eric posted a similar patch[1] last year, but the patch seems to be stuck with unrelated incomplete work. [1] https://listman.redhat.com/archives/libguestfs/2021-December/msg00065.html Signed-off-by: Nir Soffer <nsoffer(a)redhat.com&gt; --- generator/GoLang.ml | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/generator/GoLang.ml b/generator/GoLang.ml index eb3aa263..73838199 100644 --- a/generator/GoLang.ml +++ b/generator/GoLang.ml @@ -1,13 +1,13 @@ (* hey emacs, this is OCaml code: -*- tuareg -*- *) (* nbd client library in userspace: generator - * Copyright (C) 2013-2020 Red Hat Inc. + * Copyright (C) 2013-2022 Red Hat Inc. * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2 of the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. @@ -508,24 +508,24 @@ package libnbd #include \"wrappers.h\" */ import \"C\" import \"unsafe\" /* Closures. */ func copy_uint32_array (entries *C.uint32_t, count C.size_t) []uint32 { ret := make([]uint32, int (count)) - for i := 0; i < int (count); i++ { - entry := (*C.uint32_t) (unsafe.Pointer(uintptr(unsafe.Pointer(entries)) + (unsafe.Sizeof(*entries) * uintptr(i)))) - ret[i] = uint32 (*entry) - } + // See https://github.com/golang/go/wiki/cgo#turning-c-arrays-into-go-slices + // TODO: Use unsafe.Slice() when we require Go 1.17. + s := (*[1<<30]uint32)(unsafe.Pointer(entries))[:count:count] + copy(ret, s) return ret } "; List.iter ( fun { cbname; cbargs } -> let uname = camel_case cbname in pr "type %sCallback func (" uname; let comma = ref false in List.iter (