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slight simplification in 'xorshift128plus'

This commit is contained in:
Roberto Ierusalimschy 2018-03-09 12:05:13 -03:00
parent 80ae1c1c16
commit 0b3db69e41
1 changed files with 11 additions and 9 deletions
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20
lmathlib.c
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@ -1,5 +1,5 @@
/* /*
** $Id: lmathlib.c,v 1.120 2018/03/05 14:07:48 roberto Exp roberto $ ** $Id: lmathlib.c,v 1.121 2018/03/09 14:56:25 roberto Exp roberto $
** Standard mathematical library ** Standard mathematical library
** See Copyright Notice in lua.h ** See Copyright Notice in lua.h
*/ */
@ -268,7 +268,7 @@ static I xorshift128plus (I *state) {
I y = state[1]; I y = state[1];
state[0] = y; state[0] = y;
x ^= x << 23; x ^= x << 23;
state[1] = x ^ y ^ (x >> 18) ^ (y >> 5); state[1] = (x ^ (x >> 18)) ^ (y ^ (y >> 5));
return state[1] + y; return state[1] + y;
} }
@ -318,12 +318,14 @@ static I pack (int x1, int x2) {
return result; return result;
} }
static I Ishl (I i, int n) { /* i ^ (i << n) */
return pack((i.x1 << n) | (i.x2 >> (32 - n)), i.x2 << n); static I Ixorshl (I i, int n) {
return pack(i.x1 ^ ((i.x1 << n) | (i.x2 >> (32 - n))), i.x2 ^ (i.x2 << n));
} }
static I Ishr (I i, int n) { /* i ^ (i >> n) */
return pack(i.x1 >> n, (i.x2 >> n) | (i.x1 << (32 - n))); static I Ixorshr (I i, int n) {
return pack(i.x1 ^ (i.x1 >> n), i.x2 ^ ((i.x2 >> n) | (i.x1 << (32 - n))));
} }
static I Ixor (I i1, I i2) { static I Ixor (I i1, I i2) {
@ -345,9 +347,9 @@ static I xorshift128plus (I *state) {
I x = state[0]; I x = state[0];
I y = state[1]; I y = state[1];
state[0] = y; state[0] = y;
x = Ixor(x, Ishl(x, 23)); /* x ^= x << 23; */ x = Ixorshl(x, 23); /* x ^= x << 23; */
/* s[1] = x ^ y ^ (x >> 18) ^ (y >> 5); */ /* state[1] = (x ^ (x >> 18)) ^ (y ^ (y >> 5)); */
state[1] = Ixor(Ixor(Ixor(x, y), Ishr(x, 18)), Ishr(y, 5)); state[1] = Ixor(Ixorshr(x, 18), Ixorshr(y, 5));
return Iadd(state[1], y); /* return state[1] + y; */ return Iadd(state[1], y); /* return state[1] + y; */
} }