#include <stdio.h>
#include <assert.h>
-#define MAX_STEP_BITS (sizeof(size_t)*CHAR_BIT)
+#define SIZET_BITS (sizeof(size_t)*CHAR_BIT)
/* We use power of 2 steps. I tried being tricky, but it got buggy. */
struct tally {
static unsigned bucket_of(ssize_t min, unsigned step_bits, ssize_t val)
{
/* Don't over-shift. */
- if (step_bits == MAX_STEP_BITS)
+ if (step_bits == SIZET_BITS)
return 0;
- assert(step_bits < MAX_STEP_BITS);
+ assert(step_bits < SIZET_BITS);
return (size_t)(val - min) >> step_bits;
}
static ssize_t bucket_min(ssize_t min, unsigned step_bits, unsigned b)
{
/* Don't over-shift. */
- if (step_bits == MAX_STEP_BITS)
+ if (step_bits == SIZET_BITS)
return min;
- assert(step_bits < MAX_STEP_BITS);
+ assert(step_bits < SIZET_BITS);
return min + ((ssize_t)b << step_bits);
}
return divls64(tally->total[1], tally->total[0], count);
}
+ssize_t tally_total(const struct tally *tally, ssize_t *overflow)
+{
+ if (overflow) {
+ *overflow = tally->total[1];
+ return tally->total[0];
+ }
+
+ /* If result is negative, make sure we can represent it. */
+ if (tally->total[1] & (1 << (SIZET_BITS-1))) {
+ /* Must have only underflowed once, and must be able to
+ * represent result at ssize_t. */
+ if ((~tally->total[1])+1 != 0
+ || (ssize_t)tally->total[0] >= 0) {
+ /* Underflow, return minimum. */
+ return (ssize_t)((size_t)1 << (SIZET_BITS - 1));
+ }
+ } else {
+ /* Result is positive, must not have overflowed, and must be
+ * able to represent as ssize_t. */
+ if (tally->total[1] || (ssize_t)tally->total[0] < 0) {
+ /* Overflow. Return maximum. */
+ return (ssize_t)~((size_t)1 << (SIZET_BITS - 1));
+ }
+ }
+ return tally->total[0];
+}
+
static ssize_t bucket_range(const struct tally *tally, unsigned b, size_t *err)
{
ssize_t min, max;
*/
ssize_t tally_mean(const struct tally *tally);
+/**
+ * tally_total - the total value passed to tally_add.
+ * @tally: the tally structure.
+ * @overflow: the overflow value (or NULL).
+ *
+ * If your total can't overflow a ssize_t, you don't need @overflow.
+ * Otherwise, @overflow is the upper ssize_t, and the return value should
+ * be treated as the lower size_t (ie. the sign bit is in @overflow).
+ */
+ssize_t tally_total(const struct tally *tally, ssize_t *overflow);
+
/**
* tally_approx_median - the approximate median value passed to tally_add.
* @tally: the tally structure.
--- /dev/null
+#include <ccan/tally/tally.c>
+#include <ccan/tap/tap.h>
+
+int main(void)
+{
+ struct tally *tally;
+ ssize_t total, overflow;
+ ssize_t min, max;
+
+ max = (ssize_t)~(1ULL << (sizeof(max)*CHAR_BIT - 1));
+ min = (ssize_t)(1ULL << (sizeof(max)*CHAR_BIT - 1));
+
+ plan_tests(15);
+
+ /* Simple case. */
+ tally = tally_new(0);
+ tally_add(tally, min);
+ ok1(tally_total(tally, NULL) == min);
+ ok1(tally_total(tally, &overflow) == min);
+ ok1(overflow == -1);
+
+ /* Underflow. */
+ tally_add(tally, min);
+ total = tally_total(tally, &overflow);
+ ok1(overflow == -1);
+ ok1((size_t)total == 0);
+ ok1(tally_total(tally, NULL) == min);
+ free(tally);
+
+ /* Simple case. */
+ tally = tally_new(0);
+ tally_add(tally, max);
+ ok1(tally_total(tally, NULL) == max);
+ ok1(tally_total(tally, &overflow) == max);
+ ok1(overflow == 0);
+
+ /* Overflow into sign bit... */
+ tally_add(tally, max);
+ total = tally_total(tally, &overflow);
+ ok1(overflow == 0);
+ ok1((size_t)total == 0xFFFFFFFE);
+ ok1(tally_total(tally, NULL) == max);
+
+ /* Overflow into upper size_t. */
+ tally_add(tally, max);
+ total = tally_total(tally, &overflow);
+ ok1(overflow == 1);
+ ok1((size_t)total == 0x7FFFFFFD);
+ ok1(tally_total(tally, NULL) == max);
+ free(tally);
+
+ return exit_status();
+}