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Beautify ISAAC's mixing arithmetic #30455

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Dec 20, 2015
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Beautify ISAAC's mixing arithmetic #30455

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78 changes: 62 additions & 16 deletions src/librand/isaac.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -77,14 +77,37 @@ impl IsaacRng {

macro_rules! mix {
() => {{
a=a^(b<<11); d=d+a; b=b+c;
b=b^(c>>2); e=e+b; c=c+d;
c=c^(d<<8); f=f+c; d=d+e;
d=d^(e>>16); g=g+d; e=e+f;
e=e^(f<<10); h=h+e; f=f+g;
f=f^(g>>4); a=a+f; g=g+h;
g=g^(h<<8); b=b+g; h=h+a;
h=h^(a>>9); c=c+h; a=a+b;
a = a ^ (b << 11);
d = d + a;
b = b + c;
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Why aren't all of these a ^= b << 11;, d += a;, b += c; etc.?

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I initially tried that, but apparently arithmetic assignment operators aren't defined for Wrapping types like these. I imagine they will be eventually - I can't imagine why that wouldn't be simple.

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Oh, I didn't realize those were Wrapping. I guess that's a bug, because we have the traits now.


b = b ^ (c >> 2);
e = e + b;
c = c + d;

c = c ^ (d << 8);
f = f + c;
d = d + e;

d = d ^ (e >> 16);
g = g + d;
e = e + f;

e = e ^ (f << 10);
h = h + e;
f = f + g;

f = f ^ (g >> 4);
a = a + f;
g = g + h;

g = g ^ (h << 8);
b = b + g;
h = h + a;

h = h ^ (a >> 9);
c = c + h;
a = a + b;
}}
}

Expand Down Expand Up @@ -337,14 +360,37 @@ impl Isaac64Rng {

macro_rules! mix {
() => {{
a=a-e; f=f^(h>>9); h=h+a;
b=b-f; g=g^(a<<9); a=a+b;
c=c-g; h=h^(b>>23); b=b+c;
d=d-h; a=a^(c<<15); c=c+d;
e=e-a; b=b^(d>>14); d=d+e;
f=f-b; c=c^(e<<20); e=e+f;
g=g-c; d=d^(f>>17); f=f+g;
h=h-d; e=e^(g<<14); g=g+h;
a = a - e;
f = f ^ (h >> 9);
h = h + a;

b = b - f;
g = g ^ (a << 9);
a = a + b;

c = c - g;
h = h ^ (b >> 23);
b = b + c;

d = d - h;
a = a ^ (c << 15);
c = c + d;

e = e - a;
b = b ^ (d >> 14);
d = d + e;

f = f - b;
c = c ^ (e << 20);
e = e + f;

g = g - c;
d = d ^ (f >> 17);
f = f + g;

h = h - d;
e = e ^ (g << 14);
g = g + h;
}}
}

Expand Down