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* sort.c (quicksort): Added INC parameter for non-contigous

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vectors.
(quicksort1): New, for contigous vectors.  Both functions are
generated from the same code by including "quicksort.i.c".
(scm_restricted_vector_sort_x): Call one of quicksort and
quicksort1, depending on increment of vector.
(scm_sort): Simply call scm_sort_x on a copy of the list or
vector.
(scm_merge_vector_x, scm_merge_vector_step): Changed indices to
size_t, added inc parameter.
(scm_stable_sort_x): Allocate temporary storage as Scheme vector
so that it doesn't leak.
(scm_stable_sort): Simply call scm_stable_sort_x on a copy of the
list or vector.

* tags.h, weaks.c, vports.c, hashtab.c, convert.c, sort.c: Use new
vector elements API or simple vector API, as appropriate.  Removed
SCM_HAVE_ARRAYS ifdefery.  Replaced all uses of
SCM_HASHTABLE_BUCKETS with SCM_HASHTABLE_BUCKET.
This commit is contained in:
Marius Vollmer 2005-01-02 20:45:07 +00:00
parent 5d916ba3f0
commit cb26f5696c
1 changed files with 83 additions and 348 deletions
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421
libguile/sort.c
View file

@ -40,239 +40,25 @@
#include "libguile/vectors.h" #include "libguile/vectors.h"
#include "libguile/lang.h" #include "libguile/lang.h"
#include "libguile/async.h" #include "libguile/async.h"
#include "libguile/dynwind.h"
#include "libguile/validate.h" #include "libguile/validate.h"
#include "libguile/sort.h" #include "libguile/sort.h"
/* The routine quicksort was extracted from the GNU C Library qsort.c /* We have two quicksort variants: one for contigous vectors and one
written by Douglas C. Schmidt (schmidt@ics.uci.edu) for vectors with arbitrary increments between elements. Note that
and adapted to guile by adding an extra pointer less increments can be negative.
to quicksort by Roland Orre <orre@nada.kth.se>.
The reason to do this instead of using the library function qsort
was to avoid dependency of the ANSI-C extensions for local functions
and also to avoid obscure pool based solutions.
This sorting routine is not much more efficient than the stable
version but doesn't consume extra memory.
*/ */
#define SWAP(a, b) do { const SCM _tmp = a; a = b; b = _tmp; } while (0) #define NAME quicksort1
#define INC_PARAM /* empty */
#define INC 1
/* Order size using quicksort. This implementation incorporates #include "libguile/quicksort.i.c"
four optimizations discussed in Sedgewick:
1. Non-recursive, using an explicit stack of pointer that store the next
array partition to sort. To save time, this maximum amount of space
required to store an array of MAX_SIZE_T is allocated on the stack.
Assuming a bit width of 32 bits for size_t, this needs only
32 * sizeof (stack_node) == 128 bytes. Pretty cheap, actually.
2. Chose the pivot element using a median-of-three decision tree. This
reduces the probability of selecting a bad pivot value and eliminates
certain extraneous comparisons.
3. Only quicksorts NR_ELEMS / MAX_THRESH partitions, leaving insertion sort
to order the MAX_THRESH items within each partition. This is a big win,
since insertion sort is faster for small, mostly sorted array segments.
4. The larger of the two sub-partitions is always pushed onto the
stack first, with the algorithm then concentrating on the
smaller partition. This *guarantees* no more than log (n)
stack size is needed (actually O(1) in this case)! */
/* Discontinue quicksort algorithm when partition gets below this size.
* This particular magic number was chosen to work best on a Sun 4/260. */
#define MAX_THRESH 4
/* Inline stack abstraction: The stack size for quicksorting at most as many
* elements as can be given by a value of type size_t is, as described above,
* log (MAX_SIZE_T), which is the number of bits of size_t. More accurately,
* we would only need ceil (log (MAX_SIZE_T / MAX_THRESH)), but this is
* ignored below. */
/* Stack node declarations used to store unfulfilled partition obligations. */
typedef struct {
size_t lo;
size_t hi;
} stack_node;
#define STACK_SIZE (8 * sizeof (size_t)) /* assume 8 bit char */
#define PUSH(low, high) ((void) ((top->lo = (low)), (top->hi = (high)), ++top))
#define POP(low, high) ((void) (--top, (low = top->lo), (high = top->hi)))
#define STACK_NOT_EMPTY (stack < top)
static void
quicksort (SCM *const base_ptr, size_t nr_elems, scm_t_trampoline_2 cmp, SCM less)
{
static const char s_buggy_less[] = "buggy less predicate used when sorting";
if (nr_elems == 0)
/* Avoid lossage with unsigned arithmetic below. */
return;
if (nr_elems > MAX_THRESH)
{
size_t lo = 0;
size_t hi = nr_elems - 1;
stack_node stack[STACK_SIZE];
stack_node *top = stack + 1;
while (STACK_NOT_EMPTY)
{
size_t left;
size_t right;
size_t mid = lo + (hi - lo) / 2;
SCM pivot;
/* Select median value from among LO, MID, and HI. Rearrange
LO and HI so the three values are sorted. This lowers the
probability of picking a pathological pivot value and
skips a comparison for both the left and right. */
SCM_TICK;
if (scm_is_true ((*cmp) (less, base_ptr[mid], base_ptr[lo])))
SWAP (base_ptr[mid], base_ptr[lo]);
if (scm_is_true ((*cmp) (less, base_ptr[hi], base_ptr[mid])))
SWAP (base_ptr[mid], base_ptr[hi]);
else
goto jump_over;
if (scm_is_true ((*cmp) (less, base_ptr[mid], base_ptr[lo])))
SWAP (base_ptr[mid], base_ptr[lo]);
jump_over:;
pivot = base_ptr[mid];
left = lo + 1;
right = hi - 1;
/* Here's the famous ``collapse the walls'' section of quicksort.
Gotta like those tight inner loops! They are the main reason
that this algorithm runs much faster than others. */
do
{
while (scm_is_true ((*cmp) (less, base_ptr[left], pivot)))
{
left++;
/* The comparison predicate may be buggy */
if (left > hi)
scm_misc_error (NULL, s_buggy_less, SCM_EOL);
}
while (scm_is_true ((*cmp) (less, pivot, base_ptr[right])))
{
right--;
/* The comparison predicate may be buggy */
if (right < lo)
scm_misc_error (NULL, s_buggy_less, SCM_EOL);
}
if (left < right)
{
SWAP (base_ptr[left], base_ptr[right]);
left++;
right--;
}
else if (left == right)
{
left++;
right--;
break;
}
}
while (left <= right);
/* Set up pointers for next iteration. First determine whether
left and right partitions are below the threshold size. If so,
ignore one or both. Otherwise, push the larger partition's
bounds on the stack and continue sorting the smaller one. */
if ((size_t) (right - lo) <= MAX_THRESH)
{
if ((size_t) (hi - left) <= MAX_THRESH)
/* Ignore both small partitions. */
POP (lo, hi);
else
/* Ignore small left partition. */
lo = left;
}
else if ((size_t) (hi - left) <= MAX_THRESH)
/* Ignore small right partition. */
hi = right;
else if ((right - lo) > (hi - left))
{
/* Push larger left partition indices. */
PUSH (lo, right);
lo = left;
}
else
{
/* Push larger right partition indices. */
PUSH (left, hi);
hi = right;
}
}
}
/* Once the BASE_PTR array is partially sorted by quicksort the rest is
completely sorted using insertion sort, since this is efficient for
partitions below MAX_THRESH size. BASE_PTR points to the beginning of the
array to sort, and END idexes the very last element in the array (*not*
one beyond it!). */
{
size_t tmp = 0;
size_t end = nr_elems - 1;
size_t thresh = min (end, MAX_THRESH);
size_t run;
/* Find smallest element in first threshold and place it at the
array's beginning. This is the smallest array element,
and the operation speeds up insertion sort's inner loop. */
for (run = tmp + 1; run <= thresh; run++)
if (scm_is_true ((*cmp) (less, base_ptr[run], base_ptr[tmp])))
tmp = run;
if (tmp != 0)
SWAP (base_ptr[tmp], base_ptr[0]);
/* Insertion sort, running from left-hand-side up to right-hand-side. */
run = 1;
while (++run <= end)
{
SCM_TICK;
tmp = run - 1;
while (scm_is_true ((*cmp) (less, base_ptr[run], base_ptr[tmp])))
{
/* The comparison predicate may be buggy */
if (tmp == 0)
scm_misc_error (NULL, s_buggy_less, SCM_EOL);
tmp--;
}
tmp++;
if (tmp != run)
{
SCM to_insert = base_ptr[run];
size_t hi, lo;
for (hi = lo = run; --lo >= tmp; hi = lo)
base_ptr[hi] = base_ptr[lo];
base_ptr[hi] = to_insert;
}
}
}
}
#define NAME quicksort
#define INC_PARAM ssize_t inc,
#define INC inc
#include "libguile/quicksort.i.c"
static scm_t_trampoline_2 static scm_t_trampoline_2
compare_function (SCM less, unsigned int arg_nr, const char* fname) compare_function (SCM less, unsigned int arg_nr, const char* fname)
@ -283,11 +69,6 @@ compare_function (SCM less, unsigned int arg_nr, const char* fname)
} }
/* Question: Is there any need to make this a more general array sort?
It is probably enough to manage the vector type. */
/* endpos equal as for substring, i.e. endpos is not included. */
/* More natural with length? */
SCM_DEFINE (scm_restricted_vector_sort_x, "restricted-vector-sort!", 4, 0, 0, SCM_DEFINE (scm_restricted_vector_sort_x, "restricted-vector-sort!", 4, 0, 0,
(SCM vec, SCM less, SCM startpos, SCM endpos), (SCM vec, SCM less, SCM startpos, SCM endpos),
"Sort the vector @var{vec}, using @var{less} for comparing\n" "Sort the vector @var{vec}, using @var{less} for comparing\n"
@ -299,17 +80,18 @@ SCM_DEFINE (scm_restricted_vector_sort_x, "restricted-vector-sort!", 4, 0, 0,
{ {
const scm_t_trampoline_2 cmp = compare_function (less, 2, FUNC_NAME); const scm_t_trampoline_2 cmp = compare_function (less, 2, FUNC_NAME);
size_t vlen, spos, len; size_t vlen, spos, len;
SCM *vp; ssize_t vinc;
scm_t_array_handle handle;
SCM_VALIDATE_VECTOR (1, vec); SCM *velts;
vp = SCM_WRITABLE_VELTS (vec); /* vector pointer */
vlen = SCM_VECTOR_LENGTH (vec);
velts = scm_vector_writable_elements (vec, &handle, &vlen, &vinc);
spos = scm_to_unsigned_integer (startpos, 0, vlen); spos = scm_to_unsigned_integer (startpos, 0, vlen);
len = scm_to_unsigned_integer (endpos, spos, vlen) - spos; len = scm_to_unsigned_integer (endpos, spos, vlen) - spos;
quicksort (&vp[spos], len, cmp, less); if (vinc == 1)
scm_remember_upto_here_1 (vec); quicksort1 (velts + spos*vinc, len, cmp, less);
else
quicksort (velts + spos*vinc, len, vinc, cmp, less);
return SCM_UNSPECIFIED; return SCM_UNSPECIFIED;
} }
@ -330,7 +112,6 @@ SCM_DEFINE (scm_sorted_p, "sorted?", 2, 0, 0,
const scm_t_trampoline_2 cmp = compare_function (less, 2, FUNC_NAME); const scm_t_trampoline_2 cmp = compare_function (less, 2, FUNC_NAME);
long len, j; /* list/vector length, temp j */ long len, j; /* list/vector length, temp j */
SCM item, rest; /* rest of items loop variable */ SCM item, rest; /* rest of items loop variable */
SCM const *vp;
if (SCM_NULL_OR_NIL_P (items)) if (SCM_NULL_OR_NIL_P (items))
return SCM_BOOL_T; return SCM_BOOL_T;
@ -360,22 +141,24 @@ SCM_DEFINE (scm_sorted_p, "sorted?", 2, 0, 0,
} }
else else
{ {
SCM_VALIDATE_VECTOR (1, items); scm_t_array_handle handle;
size_t i, len;
ssize_t inc;
const SCM *elts;
SCM result = SCM_BOOL_T;
vp = SCM_VELTS (items); /* vector pointer */ elts = scm_vector_elements (items, &handle, &len, &inc);
len = SCM_VECTOR_LENGTH (items);
j = len - 1; for (i = 1; i < len; i++, elts += inc)
while (j > 0)
{ {
if (scm_is_true ((*cmp) (less, vp[1], vp[0]))) if (scm_is_true ((*cmp) (less, elts[inc], elts[0])))
return SCM_BOOL_F;
else
{ {
vp++; result = SCM_BOOL_F;
j--; break;
} }
} }
return SCM_BOOL_T;
return result;
} }
return SCM_BOOL_F; return SCM_BOOL_F;
@ -596,13 +379,12 @@ SCM_DEFINE (scm_sort_x, "sort!", 2, 0, 0,
SCM_VALIDATE_LIST_COPYLEN (1, items, len); SCM_VALIDATE_LIST_COPYLEN (1, items, len);
return scm_merge_list_step (&items, cmp, less, len); return scm_merge_list_step (&items, cmp, less, len);
} }
else if (SCM_VECTORP (items)) else if (scm_is_vector (items))
{ {
len = SCM_VECTOR_LENGTH (items);
scm_restricted_vector_sort_x (items, scm_restricted_vector_sort_x (items,
less, less,
scm_from_int (0), scm_from_int (0),
scm_from_long (len)); scm_vector_length (items));
return items; return items;
} }
else else
@ -622,29 +404,9 @@ SCM_DEFINE (scm_sort, "sort", 2, 0, 0,
return items; return items;
if (scm_is_pair (items)) if (scm_is_pair (items))
{ return scm_sort_x (scm_list_copy (items), less);
const scm_t_trampoline_2 cmp = compare_function (less, 2, FUNC_NAME); else if (scm_is_vector (items))
long len; return scm_sort_x (scm_vector_copy (items), less);
SCM_VALIDATE_LIST_COPYLEN (1, items, len);
items = scm_list_copy (items);
return scm_merge_list_step (&items, cmp, less, len);
}
#if SCM_HAVE_ARRAYS
/* support ordinary vectors even if arrays not available? */
else if (SCM_VECTORP (items))
{
long len = SCM_VECTOR_LENGTH (items);
SCM sortvec = scm_make_uve (len, scm_array_prototype (items));
scm_array_copy_x (items, sortvec);
scm_restricted_vector_sort_x (sortvec,
less,
scm_from_int (0),
scm_from_long (len));
return sortvec;
}
#endif
else else
SCM_WRONG_TYPE_ARG (1, items); SCM_WRONG_TYPE_ARG (1, items);
} }
@ -652,68 +414,62 @@ SCM_DEFINE (scm_sort, "sort", 2, 0, 0,
static void static void
scm_merge_vector_x (SCM vec, scm_merge_vector_x (SCM *vec,
SCM *temp, SCM *temp,
scm_t_trampoline_2 cmp, scm_t_trampoline_2 cmp,
SCM less, SCM less,
long low, size_t low,
long mid, size_t mid,
long high) size_t high,
ssize_t inc)
{ {
long it; /* Index for temp vector */ size_t it; /* Index for temp vector */
long i1 = low; /* Index for lower vector segment */ size_t i1 = low; /* Index for lower vector segment */
long i2 = mid + 1; /* Index for upper vector segment */ size_t i2 = mid + 1; /* Index for upper vector segment */
#define VEC(i) vec[(i)*inc]
/* Copy while both segments contain more characters */ /* Copy while both segments contain more characters */
for (it = low; (i1 <= mid) && (i2 <= high); ++it) for (it = low; (i1 <= mid) && (i2 <= high); ++it)
{ {
/* if (scm_is_true ((*cmp) (less, VEC(i2), VEC(i1))))
Every call of LESS might invoke GC. For full correctness, we temp[it] = VEC(i2++);
should reset the generation of vecbase and tempbase between
every call of less.
*/
register SCM *vp = SCM_WRITABLE_VELTS(vec);
if (scm_is_true ((*cmp) (less, vp[i2], vp[i1])))
temp[it] = vp[i2++];
else else
temp[it] = vp[i1++]; temp[it] = VEC(i1++);
} }
{ {
register SCM *vp = SCM_WRITABLE_VELTS(vec);
/* Copy while first segment contains more characters */ /* Copy while first segment contains more characters */
while (i1 <= mid) while (i1 <= mid)
temp[it++] = vp[i1++]; temp[it++] = VEC(i1++);
/* Copy while second segment contains more characters */ /* Copy while second segment contains more characters */
while (i2 <= high) while (i2 <= high)
temp[it++] = vp[i2++]; temp[it++] = VEC(i2++);
/* Copy back from temp to vp */ /* Copy back from temp to vp */
for (it = low; it <= high; ++it) for (it = low; it <= high; it++)
vp[it] = temp[it]; VEC(it) = temp[it];
} }
} /* scm_merge_vector_x */ } /* scm_merge_vector_x */
static void static void
scm_merge_vector_step (SCM vp, scm_merge_vector_step (SCM *vec,
SCM *temp, SCM *temp,
scm_t_trampoline_2 cmp, scm_t_trampoline_2 cmp,
SCM less, SCM less,
long low, size_t low,
long high) size_t high,
ssize_t inc)
{ {
if (high > low) if (high > low)
{ {
long mid = (low + high) / 2; size_t mid = (low + high) / 2;
SCM_TICK; SCM_TICK;
scm_merge_vector_step (vp, temp, cmp, less, low, mid); scm_merge_vector_step (vec, temp, cmp, less, low, mid, inc);
scm_merge_vector_step (vp, temp, cmp, less, mid+1, high); scm_merge_vector_step (vec, temp, cmp, less, mid+1, high, inc);
scm_merge_vector_x (vp, temp, cmp, less, low, mid, high); scm_merge_vector_x (vec, temp, cmp, less, low, mid, high, inc);
} }
} /* scm_merge_vector_step */ } /* scm_merge_vector_step */
@ -738,19 +494,21 @@ SCM_DEFINE (scm_stable_sort_x, "stable-sort!", 2, 0, 0,
SCM_VALIDATE_LIST_COPYLEN (1, items, len); SCM_VALIDATE_LIST_COPYLEN (1, items, len);
return scm_merge_list_step (&items, cmp, less, len); return scm_merge_list_step (&items, cmp, less, len);
} }
else if (SCM_VECTORP (items)) else if (scm_is_vector (items))
{ {
SCM *temp; scm_t_array_handle temp_handle, vec_handle;
len = SCM_VECTOR_LENGTH (items); SCM temp, *temp_elts, *vec_elts;
size_t len;
ssize_t inc;
/* vec_elts = scm_vector_writable_elements (items, &vec_handle,
the following array does not contain any new references to &len, &inc);
SCM objects, so we can get away with allocing it on the heap. temp = scm_c_make_vector (len, SCM_UNDEFINED);
*/ temp_elts = scm_vector_writable_elements (temp, &temp_handle,
temp = scm_malloc (len * sizeof(SCM)); NULL, NULL);
scm_merge_vector_step (vec_elts, temp_elts, cmp, less, 0, len-1, inc);
scm_merge_vector_step (items, temp, cmp, less, 0, len - 1);
free(temp);
return items; return items;
} }
else else
@ -766,33 +524,10 @@ SCM_DEFINE (scm_stable_sort, "stable-sort", 2, 0, 0,
"This is a stable sort.") "This is a stable sort.")
#define FUNC_NAME s_scm_stable_sort #define FUNC_NAME s_scm_stable_sort
{ {
const scm_t_trampoline_2 cmp = compare_function (less, 2, FUNC_NAME);
if (SCM_NULL_OR_NIL_P (items))
return items;
if (scm_is_pair (items)) if (scm_is_pair (items))
{ return scm_stable_sort_x (scm_list_copy (items), less);
long len; /* list/vector length */ else if (scm_is_vector (items))
return scm_stable_sort_x (scm_vector_copy (items), less);
SCM_VALIDATE_LIST_COPYLEN (1, items, len);
items = scm_list_copy (items);
return scm_merge_list_step (&items, cmp, less, len);
}
#if SCM_HAVE_ARRAYS
/* support ordinary vectors even if arrays not available? */
else if (SCM_VECTORP (items))
{
long len = SCM_VECTOR_LENGTH (items);
SCM *temp = scm_malloc (len * sizeof (SCM));
SCM retvec = scm_make_uve (len, scm_array_prototype (items));
scm_array_copy_x (items, retvec);
scm_merge_vector_step (retvec, temp, cmp, less, 0, len - 1);
free (temp);
return retvec;
}
#endif
else else
SCM_WRONG_TYPE_ARG (1, items); SCM_WRONG_TYPE_ARG (1, items);
} }