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syscall: document float arguments and results on windows/amd64

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Updates #6510.
Updates #37273.

Change-Id: Id2732fcff0a0c5e4a324cd33ef995c7e528f5e1a
Reviewed-on: https://go-review.googlesource.com/c/go/+/236562
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Austin Clements 2020-06-04 11:17:49 -04:00
parent 7e47757324
commit 07ced37013
2 changed files with 12 additions and 4 deletions
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6
doc/go1.15.html
View File

@ -629,9 +629,9 @@ TODO
</p>
<p><!-- CL 220578 -->
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 <a href="/pkg/syscall/#Proc.Call">now possible</a> to call
system calls that return floating point values
on <code>windows/amd64</code>.
</p>
</dd>
</dl>

10
src/syscall/dll_windows.go
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@ -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: