From 07ced37013b6b3bdb9cd02def52821a09a4e9c58 Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Thu, 4 Jun 2020 11:17:49 -0400 Subject: [PATCH] syscall: document float arguments and results on windows/amd64 Updates #6510. Updates #37273. Change-Id: Id2732fcff0a0c5e4a324cd33ef995c7e528f5e1a Reviewed-on: https://go-review.googlesource.com/c/go/+/236562 Reviewed-by: Brad Fitzpatrick --- doc/go1.15.html | 6 +++--- src/syscall/dll_windows.go | 10 +++++++++- 2 files changed, 12 insertions(+), 4 deletions(-) diff --git a/doc/go1.15.html b/doc/go1.15.html index 15f56eef9d..93804a9d27 100644 --- a/doc/go1.15.html +++ b/doc/go1.15.html @@ -629,9 +629,9 @@ TODO

- It is now possible to call system calls that return floating - point values on windows/amd64. - TODO: Point to (write?) documentation on how to do this. + It is now possible to call + system calls that return floating point values + on windows/amd64.

diff --git a/src/syscall/dll_windows.go b/src/syscall/dll_windows.go index 819bc5eeb8..c54feec56a 100644 --- a/src/syscall/dll_windows.go +++ b/src/syscall/dll_windows.go @@ -163,7 +163,15 @@ func (p *Proc) Addr() uintptr { // The returned error is always non-nil, constructed from the result of GetLastError. // Callers must inspect the primary return value to decide whether an error occurred // (according to the semantics of the specific function being called) before consulting -// the error. The error will be guaranteed to contain syscall.Errno. +// the error. The error always has type syscall.Errno. +// +// On amd64, Call can pass and return floating-point values. To pass +// an argument x with C type "float", use +// uintptr(math.Float32bits(x)). To pass an argument with C type +// "double", use uintptr(math.Float64bits(x)). Floating-point return +// values are returned in r2. The return value for C type "float" is +// math.Float32frombits(uint32(r2)). For C type "double", it is +// math.Float64frombits(uint64(r2)). func (p *Proc) Call(a ...uintptr) (r1, r2 uintptr, lastErr error) { switch len(a) { case 0: -- 2.48.1