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Several details in code (e.g., moving a variable to the most inner
scope that encloses its uses), comments, parameter names, extra tests.
This commit is contained in:
Roberto Ierusalimschy
2020-02-27 12:59:22 -03:00
parent 9b7987a9d1
commit 6eb53b7526
13 changed files with 52 additions and 45 deletions
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28
lmathlib.c
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@@ -522,16 +522,18 @@ typedef struct {
** Project the random integer 'ran' into the interval [0, n].
** Because 'ran' has 2^B possible values, the projection can only be
** uniform when the size of the interval is a power of 2 (exact
** division). To get a uniform projection into [0, n], we first compute
** 'lim', the smallest Mersenne number not smaller than 'n'. We then
** project 'ran' into the interval [0, lim]. If the result is inside
** [0, n], we are done. Otherwise, we try with another 'ran', until we
** have a result inside the interval.
** division). Otherwise, to get a uniform projection into [0, n], we
** first compute 'lim', the smallest Mersenne number not smaller than
** 'n'. We then project 'ran' into the interval [0, lim]. If the result
** is inside [0, n], we are done. Otherwise, we try with another 'ran',
** until we have a result inside the interval.
*/
static lua_Unsigned project (lua_Unsigned ran, lua_Unsigned n,
RanState *state) {
lua_Unsigned lim = n;
if ((lim & (lim + 1)) > 0) { /* 'lim + 1' is not a power of 2? */
if ((n & (n + 1)) == 0) /* is 'n + 1' a power of 2? */
return ran & n; /* no bias */
else {
lua_Unsigned lim = n;
/* compute the smallest (2^b - 1) not smaller than 'n' */
lim |= (lim >> 1);
lim |= (lim >> 2);
@@ -541,13 +543,13 @@ static lua_Unsigned project (lua_Unsigned ran, lua_Unsigned n,
#if (LUA_MAXUNSIGNED >> 31) >= 3
lim |= (lim >> 32); /* integer type has more than 32 bits */
#endif
lua_assert((lim & (lim + 1)) == 0 /* 'lim + 1' is a power of 2, */
&& lim >= n /* not smaller than 'n', */
&& (lim >> 1) < n); /* and it is the smallest one */
while ((ran &= lim) > n) /* project 'ran' into [0..lim] */
ran = I2UInt(nextrand(state->s)); /* not inside [0..n]? try again */
return ran;
}
lua_assert((lim & (lim + 1)) == 0 /* 'lim + 1' is a power of 2, */
&& lim >= n /* not smaller than 'n', */
&& (lim == 0 || (lim >> 1) < n)); /* and it is the smallest one */
while ((ran &= lim) > n) /* project 'ran' into [0..lim] */
ran = I2UInt(nextrand(state->s)); /* not inside [0..n]? try again */
return ran;
}