• Alberto (57/57) Feb 12 2007 I have some problem casting a struct to void[]:
• Deewiant (20/32) Feb 12 2007 I came up with the following. It seems idiomatic to me, but there might ...
• Frits van Bommel (13/40) Feb 12 2007 That RSAEncryptedData.sizeof should be 1, since you're slicing a value

Alberto <reda zioale.it> writes:

I have some problem casting a struct to void[]:

const ushort RSA_ENC_LEN =256;

struct RSAEncryptedData {
  ubyte encoding[RSA_ENC_LEN];
}

struct Signature {
  ubyte sig[RSA_ENC_LEN];
}

class RSA {
  ...
  Signature sign(void[] block, int type=Hash.SHA512);
  bool verifySig(void[] block, Signature sig, int type=Hash.SHA512);
  ...
}

int main() {
	ubyte[32] sessionkey;
	int ret;
	
	aes128 aes = new aes128(Bits256);
	aes.setRandomKey();
	sessionkey[0..$] = aes.getKey();

	RSA  rsatest = new RSA();
	RSAEncryptedData buf = rsatest.encryptWithPublicKey(sessionkey);
	

	Signature sig = rsatest.sign(cast(void[])buf.encoding, Hash.SHA512);
	ret = rsatest.verifySig(cast(void[])buf.encoding, sig, Hash.SHA512);
	assert(ret == true);
	

	void[] a;
	a.length = RSAEncryptedData.sizeof;
	memcpy(cast(void *)a, cast(void *)&buf, a.length);
	Signature sig2 = rsatest.sign(a, Hash.SHA512);
	ret = rsatest.verifySig(a, sig2, Hash.SHA512);	
	assert(ret == true);
	

	Signature sig3 =
rsatest.sign(cast(void[])((&buf)[0..RSAEncryptedData.sizeof]), Hash.SHA512);
	ret =
rsatest.verifySig(cast(void[])((&buf)[0..RSAEncryptedData.sizeof]),
sig3, Hash.SHA512);
	assert(ret == true);

	return 0;
}

I got an Assertion failure on the 3° assert, where I have tried to cast
buf directly to void[].
In general, if I have something like this:

struct pippo {
   ushort a;
   ushort b;
   ubyte[170] c;
   uint d;
}

void do_something(void []);

Deewiant <deewiant.doesnotlike.spam gmail.com> writes:

Alberto wrote:
 In general, if I have something like this:
 
 struct pippo {
    ushort a;
    ushort b;
    ubyte[170] c;
    uint d;
 }
 
 void do_something(void []);
 


I came up with the following. It seems idiomatic to me, but there might be
something smarter:

struct pippo {
   ushort a;
   ushort b;
   ubyte[170] c;
   uint d;
}

void do_something(void[] foo) {
	pippo* p = cast(pippo*)foo.ptr;
	assert (p.d == 2);
}

void main() {
	pippo p;
	p.d = 2;
	do_something((&p)[0..pippo.sizeof]);
}

-- 
Remove ".doesnotlike.spam" from the mail address.

Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:

Alberto wrote:
 I have some problem casting a struct to void[]:
 

[snip]

 	Signature sig3 =
 rsatest.sign(cast(void[])((&buf)[0..RSAEncryptedData.sizeof]), Hash.SHA512);
 	ret =
 rsatest.verifySig(cast(void[])((&buf)[0..RSAEncryptedData.sizeof]),
 sig3, Hash.SHA512);
 	assert(ret == true);

That RSAEncryptedData.sizeof should be 1, since you're slicing a value 
of type RSAEncryptedData*.

 
 	return 0;
 }
 
 I got an Assertion failure on the 3° assert, where I have tried to cast
 buf directly to void[].
 In general, if I have something like this:
 
 struct pippo {
    ushort a;
    ushort b;
    ubyte[170] c;
    uint d;
 }
 
 void do_something(void []);
 


My preferred way is something like
---
pippo somevar;
// ... initialize
do_something((&somevar)[0..1]);
---

(The inner brackets may be superfluous, but I'm not sure. My rule of 
thumb in such cases is to always put them in there, because even if the 
code does exactly the same they make it more clear what's happening)