internal/syscall/windows: correct GetACP and MultiByteToWideChar

CL 4310 introduced these functions, but their
implementation does not match with their published
documentation. Correct the implementation.

Change-Id: I285e41f9c7c5fc4e550ff59b0adb8b2bcbf6737a
Reviewed-on: https://go-review.googlesource.com/17997Reviewed-by: Yasuhiro MATSUMOTO <mattn.jp@gmail.com>
Reviewed-by: Russ Cox <rsc@golang.org>

src/internal/syscall/windows/syscall_windows.go

@@ -139,5 +139,5 @@ func Rename(oldpath, newpath string) error {
 	return MoveFileEx(from, to, MOVEFILE_REPLACE_EXISTING)
 }
 
-//sys	GetACP() (acp uint, err error) = kernel32.GetACP
-//sys	MultiByteToWideChar(codePage uint, dwFlags uint32, str *byte, nstr int32, wchar *uint16, nwchar int32) (nwrite int, err error) = kernel32.MultiByteToWideChar
+//sys	GetACP() (acp uint32) = kernel32.GetACP
+//sys	MultiByteToWideChar(codePage uint32, dwFlags uint32, str *byte, nstr int32, wchar *uint16, nwchar int32) (nwrite int32, err error) = kernel32.MultiByteToWideChar

src/internal/syscall/windows/zsyscall_windows.go

@@ -50,23 +50,16 @@ func MoveFileEx(from *uint16, to *uint16, flags uint32) (err error) {
 	return
 }
 
-func MultiByteToWideChar(codePage uint, dwFlags uint32, str *byte, nstr int32, wchar *uint16, nwchar int32) (nwrite int, err error) {
-	r0, _, e1 := syscall.Syscall6(procMultiByteToWideChar.Addr(), 6, uintptr(codePage), uintptr(dwFlags), uintptr(unsafe.Pointer(str)), uintptr(nstr), uintptr(unsafe.Pointer(wchar)), uintptr(nwchar))
-	nwrite = int(r0)
-	if nwrite == 0 {
-		if e1 != 0 {
-			err = error(e1)
-		} else {
-			err = syscall.EINVAL
-		}
-	}
+func GetACP() (acp uint32) {
+	r0, _, _ := syscall.Syscall(procGetACP.Addr(), 0, 0, 0, 0)
+	acp = uint32(r0)
 	return
 }
 
-func GetACP() (acp uint, err error) {
-	r0, _, e1 := syscall.Syscall(procGetACP.Addr(), 0, 0, 0, 0)
-	acp = uint(r0)
-	if acp == 0 {
+func MultiByteToWideChar(codePage uint32, dwFlags uint32, str *byte, nstr int32, wchar *uint16, nwchar int32) (nwrite int32, err error) {
+	r0, _, e1 := syscall.Syscall6(procMultiByteToWideChar.Addr(), 6, uintptr(codePage), uintptr(dwFlags), uintptr(unsafe.Pointer(str)), uintptr(nstr), uintptr(unsafe.Pointer(wchar)), uintptr(nwchar))
+	nwrite = int32(r0)
+	if nwrite == 0 {
 		if e1 != 0 {
 			err = error(e1)
 		} else {

src/os/file_windows.go

@@ -279,10 +279,7 @@ func (f *File) readConsole(b []byte) (n int, err error) {
 			if len(b) > 0 {
 				pmb = &mbytes[0]
 			}
-			acp, err := windows.GetACP()
-			if err != nil {
-				return 0, err
-			}
+			acp := windows.GetACP()
 			nwc, err := windows.MultiByteToWideChar(acp, 2, pmb, int32(nmb), nil, 0)
 			if err != nil {
 				return 0, err