tools/lib/list_sort.c

14 __attribute__((nonnull(2,3,4)))
50 __attribute__((nonnull(2,3,4,5)))
119  * 2:1 balanced merges.  Given two pending sublists of size 2^k, they are
120  * merged to a size-2^(k+1) list as soon as we have 2^k following elements.
122  * Thus, it will avoid cache thrashing as long as 3*2^k elements can
131  * Each time we increment "count", we set one bit (bit k) and clear
132  * bits k-1 .. 0.  Each time this happens (except the very first time
133  * for each bit, when count increments to 2^k), we merge two lists of
134  * size 2^k into one list of size 2^(k+1).
137  * 2^k, which is when we have 2^k elements pending in smaller lists,
138  * so it's safe to merge away two lists of size 2^k.
140  * After this happens twice, we have created two lists of size 2^(k+1),
141  * which will be merged into a list of size 2^(k+2) before we create
142  * a third list of size 2^(k+1), so there are never more than two pending.
144  * The number of pending lists of size 2^k is determined by the
145  * state of bit k of "count" plus two extra pieces of information:
147  * - The state of bit k-1 (when k == 0, consider bit -1 always set), and
149  *   is count >= 2^(k+1)).
153  * 0:  00x: 0 pending of size 2^k;           x pending of sizes < 2^k
154  * 1:  01x: 0 pending of size 2^k; 2^(k-1) + x pending of sizes < 2^k
155  * 2: x10x: 0 pending of size 2^k; 2^k     + x pending of sizes < 2^k
156  * 3: x11x: 1 pending of size 2^k; 2^(k-1) + x pending of sizes < 2^k
157  * 4: y00x: 1 pending of size 2^k; 2^k     + x pending of sizes < 2^k
158  * 5: y01x: 2 pending of size 2^k; 2^(k-1) + x pending of sizes < 2^k
159  * (merge and loop back to state 2)
161  * We gain lists of size 2^k in the 2->3 and 4->5 transitions (because
162  * bit k-1 is set while the more significant bits are non-zero) and
163  * merge them away in the 5->2 transition.  Note in particular that just
164  * before the 5->2 transition, all lower-order bits are 11 (state 3),
168  * lists, from smallest to largest.  If you work through cases 2 to
170  * of size 2^k varies from 2^(k-1) (cases 3 and 5 when x == 0) to
171  * 2^(k+1) - 1 (second merge of case 5 when x == 2^(k-1) - 1).
173 __attribute__((nonnull(2,3)))
197 	 *   That ensures each later final merge will be at worst 2:1.  in list_sort()