+ int prio = inc;
+ // Only query old priority if it can affect the result.
+ // This also avoids issues with integer overflow.
+ if (inc > -2*NZERO && inc < 2*NZERO)
+ prio += getpriority(PRIO_PROCESS, 0);
+ if (prio > NZERO-1) prio = NZERO-1;
+ if (prio < -NZERO) prio = -NZERO;
+ return setpriority(PRIO_PROCESS, 0, prio) ? -1 : prio;