digitalmars.D.ldc - ldc -O leads to wrong results
- salsa (101/101) Mar 09 2015 Recently I got stuck with this:
Recently I got stuck with this:
compiling following code with ldc -O generates code that doesn't
do what I expect it to do. Compiling it without optimizations
works fine. Does somebody have any idea what the problem might
be? To reproduce the bug just compile and run once with 'ldc *.d'
and once with 'ldc -O *.d'...
thanks for your help
module dcrypt.crypto.engines.Salsa20Engine;
// LDC - the LLVM D compiler (0.15.1):
// based on DMD v2.066.1 and LLVM 3.5.0
//
// to reproduce bug: run once with inline disabled and once with
inline enabled, compare results:
//
// causes wrong behaviour: ldmd ldc_inline_issue.d -O
//
public void main() {
import std.stdio;
uint[Salsa20Engine.STATE_SIZE] x;
uint[Salsa20Engine.STATE_SIZE] input;
input[0..2] = cast(const(uint[]))"abcdefgh";
Salsa20Engine.salsaCore(20, input[], x[]);
writeln(x);
}
class Salsa20Engine {
enum STATE_SIZE = 16;
/**
* Salsa20 function
*
* Params:
* rounds = number of rounds (20 in default implementation)
* input = input data
* x = output buffer where keystream gets written to
*/
public static void salsaCore(in uint rounds, in uint[] input,
uint[] x) pure nothrow nogc
in {
assert(rounds % 2 == 0 || rounds > 0, "rounds must be a even
number and > 0");
assert(input.length == STATE_SIZE, "invalid input length");
assert(x.length == STATE_SIZE, "x: invalid length");
}
body {
x[] = input[];
for (int i = rounds; i > 0; i -= 2)
{
x[ 4] ^= rotl((x[ 0]+x[12]), 7);
x[ 8] ^= rotl((x[ 4]+x[ 0]), 9);
x[12] ^= rotl((x[ 8]+x[ 4]),13);
x[ 0] ^= rotl((x[12]+x[ 8]),18);
x[ 9] ^= rotl((x[ 5]+x[ 1]), 7);
x[13] ^= rotl((x[ 9]+x[ 5]), 9);
x[ 1] ^= rotl((x[13]+x[ 9]),13);
x[ 5] ^= rotl((x[ 1]+x[13]),18);
x[14] ^= rotl((x[10]+x[ 6]), 7);
x[ 2] ^= rotl((x[14]+x[10]), 9);
x[ 6] ^= rotl((x[ 2]+x[14]),13);
x[10] ^= rotl((x[ 6]+x[ 2]),18);
x[ 3] ^= rotl((x[15]+x[11]), 7);
x[ 7] ^= rotl((x[ 3]+x[15]), 9);
x[11] ^= rotl((x[ 7]+x[ 3]),13);
x[15] ^= rotl((x[11]+x[ 7]),18);
x[ 1] ^= rotl((x[ 0]+x[ 3]), 7);
x[ 2] ^= rotl((x[ 1]+x[ 0]), 9);
x[ 3] ^= rotl((x[ 2]+x[ 1]),13);
x[ 0] ^= rotl((x[ 3]+x[ 2]),18);
x[ 6] ^= rotl((x[ 5]+x[ 4]), 7);
x[ 7] ^= rotl((x[ 6]+x[ 5]), 9);
x[ 4] ^= rotl((x[ 7]+x[ 6]),13);
x[ 5] ^= rotl((x[ 4]+x[ 7]),18);
x[11] ^= rotl((x[10]+x[ 9]), 7);
x[ 8] ^= rotl((x[11]+x[10]), 9);
x[ 9] ^= rotl((x[ 8]+x[11]),13);
x[10] ^= rotl((x[ 9]+x[ 8]),18);
x[12] ^= rotl((x[15]+x[14]), 7);
x[13] ^= rotl((x[12]+x[15]), 9);
x[14] ^= rotl((x[13]+x[12]),13);
x[15] ^= rotl((x[14]+x[13]),18);
}
// element wise addition
x[] += input[];
}
/**
* Rotate left
*
* Params:
* x = value to rotate
* y = amount to rotate x
*
* Returns: rotated x
*/
final static T rotl(T)(T x, T y) pure nothrow nogc
{
return (x << y) | (x >>> -y);
}
}
Mar 09 2015
"salsa" <salsa salsa.com> writes:Recently I got stuck with this: compiling following code with ldc -O generates code that doesn't do what I expect it to do. Compiling it without optimizations works fine. Does somebody have any idea what the problem might be? To reproduce the bug just compile and run once with 'ldc *.d' and once with 'ldc -O *.d'... x[ 4] ^= rotl((x[ 0]+x[12]), 7);...final static T rotl(T)(T x, T y) pure nothrow nogc { return (x << y) | (x >>> -y); }Hi salsa. y is 7 so (x >>> -7) yields an unspecified value because shift is negative (see TDPL 2.3.10 Shift Expression). I think results are only defined when shifting 0 to nbits-1. Here is one way to get it to work with -O: final static T rotl(T)(T x, uint y) pure nothrow nogc { enum nbits = T.sizeof*8; return (x << y) | (x >>> nbits-y); } -- Dan
Mar 09 2015
"salsa" <salsa salsa.com> 
On Tuesday, 10 March 2015 at 05:35:59 UTC, Dan Olson wrote:"salsa" <salsa salsa.com> writes:Maybe this should be explicitly said in documentation: http://dlang.org/expression.html#ShiftExpression Btw. why this is not compile error on the first place?Recently I got stuck with this: compiling following code with ldc -O generates code that doesn't do what I expect it to do. Compiling it without optimizations works fine. Does somebody have any idea what the problem might be? To reproduce the bug just compile and run once with 'ldc *.d' and once with 'ldc -O *.d'... x[ 4] ^= rotl((x[ 0]+x[12]), 7);...final static T rotl(T)(T x, T y) pure nothrow nogc { return (x << y) | (x >>> -y); }Hi salsa. y is 7 so (x >>> -7) yields an unspecified value because shift is negative (see TDPL 2.3.10 Shift Expression). I think results are only defined when shifting 0 to nbits-1.
Mar 14 2015
On Saturday, 14 March 2015 at 07:02:51 UTC, Dude wrote:Btw. why this is not compile error on the first place?It can't be compilation error, because the function doesn't see all values passed to it. It probably belongs to checked arithmetic, which is not done by default.
Mar 14 2015