Re: Sending floats using objc_msgSendv

• Subject: Re: Sending floats using objc_msgSendv
• From: Patrick Beard <email@hidden>
• Date: Thu, 11 Aug 2005 08:38:06 -0700
• Delivered-to: email@hidden
• Delivered-to: email@hidden

On Aug 11, 2005, at 12:41 AM, Nathaniel Gray wrote:

On Aug 10, 2005, at 6:56 PM, Sherm Pendley wrote:

On Aug 10, 2005, at 9:32 PM, Greg Parker wrote:

On Aug 10, 2005, at 6:02 PM, Nathaniel Gray wrote:

Is there any way to send float or double arguments to a method designated at runtime? I've tried using objc_msgSendv, casting it in various ways, and using -performv::, but nothing works.

Using objc_msgSendv() properly requires knowledge of your platform's ABI. In particular, floating-point values must be stored in a special place in the marg_list on PowerPC. objc-msg- ppc.s notes some of the details.

I think those details are pretty well hidden by the marg_* macros though. I've used method_getArgumentInfo() to get the offset of the argument, and marg_setValue() to set it before calling objc_msgSendv(). It worked fine with all sorts of types, including floats and doubles.

Really? That's exactly what I'm doing. For a test case I wrote a class OCOCTestCall with a class method

+ (float)callFloat:(float)x
{
    eprintf("Got float: %f\n", x);
    return x+1.0;
}

Then I call it with this code:

void test1_1mini() {
    id nc = NSClassFromString(@"OCOCTestCall");
    SEL sel = @selector(callFloat:);
    marg_list margs;
    int offset;
    Method method;
    const char* argtype;
    union {float f; id i;} u;

    u.f = 123.45f;

    method = class_getInstanceMethod(nc->isa, sel);
    /* Set up the marg_list */
    marg_malloc(margs, method);
    method_getArgumentInfo(method, 0, &argtype, &offset);
    marg_setValue(margs, offset, id, nc);
    method_getArgumentInfo(method, 1, &argtype, &offset);
    marg_setValue(margs, offset, SEL, sel);
    method_getArgumentInfo(method, 2, &argtype, &offset);
    marg_setValue(margs, offset, float, u.f);

/* Plain msgSendv */
u.i = objc_msgSendv(nc, sel, method_getSizeOfArguments(method), margs);
printf( "msgSendv: float u.f = %f\n", u.f );

/* Cast function type to return float */
u.f = ((float_msgSendv)objc_msgSendv)(nc, sel,
method_getSizeOfArguments(method), margs);
printf( "((float_msgSendv)objc_msgSendv): float u.f = %f\n", u.f );

    /* Send as message */
    u.i = [nc performv:sel :margs];
    printf( "[nc performv::]: Float u.f = %f\n", u.f );
}

Here's what I get:

[n8gray@golux test]$ ./ctest1
Got float: 0.000000
msgSendv: Float f = 0.000000
Got float: 0.000000
((float_msgSendv)objc_msgSendv): Float f = 1.000000
Got float: 0.000000
[nc performv::]: Float f = 0.000000

Adding this variant works just fine:

    /* Plain msgSend */
    u.f = ((float (*) (id, SEL, float))objc_msgSend)(nc, sel, u.f);
    printf( "objc_msgSend: float u.f = %f\n", u.f );

Got float: 123.449997
objc_msgSend: float u.f = 124.449997

    /* Set up the marg_list */
    marg_malloc(margs, method);
    method_getArgumentInfo(method, 0, &argtype, &offset);
    marg_setValue(margs, offset, id, nc);
    method_getArgumentInfo(method, 1, &argtype, &offset);
    marg_setValue(margs, offset, SEL, sel);
    method_getArgumentInfo(method, 2, &argtype, &offset);
    marg_setValue(margs, offset, float, u.f);
    ((double*)margs)[0] = u.f;

Got float: 123.449997
objc_msgSend: float u.f = 124.449997
Got float: 123.449997
msgSendv: float u.f = 0.000000
Got float: 123.449997
((float_msgSendv)objc_msgSendv): float u.f = 124.449997
Got float: 123.449997
[nc performv::]: Float u.f = 0.000000

You can download this source from here:

- Patrick

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