fix #H174 - ice effects on corpses are miscalculated

     Reported in August by <email deleted>, the code that handles
slower rotting for corpses on top of or buried under ice is misusing its
ROT_ICE_ADJUSTMENT factor such that a value other than the current 2 would
produce incorrect results.  Instead of multiplying by 1/N it needs to use
(N-1)/N, which happens to be the same when N is 2.  In a second message he
asked about why putting a corpse on ice starts out by subtracting from its
age to make it older, and it took me a while to decide that that is correct
behavior.

     No effect on game play since ROT_ICE_ADJUSTMENT remains set to 2.

diff --git a/src/mkobj.c b/src/mkobj.c
index 511de4073be75d1b1a0bcc466f658299f823fc64..af7fe366dd2cfae53f6354bc1ee771a96709b466 100644 (file)
--- a/src/mkobj.c
+++ b/src/mkobj.c
@@ -1,4 +1,4 @@
-/*     SCCS Id: @(#)mkobj.c    3.5     2007/02/17      */
+/*     SCCS Id: @(#)mkobj.c    3.5     2007/04/04      */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -1462,7 +1462,7 @@ struct obj *otmp;
     if (otmp->otyp == CORPSE && otmp->on_ice) {
        /* Adjust the age; must be same as obj_timer_checks() for off ice*/
        age = monstermoves - otmp->age;
-       retval = otmp->age + (age / ROT_ICE_ADJUSTMENT);
+       retval += age * (ROT_ICE_ADJUSTMENT-1) / ROT_ICE_ADJUSTMENT;
 #ifdef DEBUG_EFFECTS
        pline_The("%s age has ice modifications:otmp->age = %ld, returning %ld.",
                s_suffix(doname(otmp)),otmp->age, retval);
@@ -1503,7 +1503,11 @@ int force;       /* 0 = no force so do checks, <0 = force off, >0 force on */
            /* Adjust the time remaining */
            tleft *= ROT_ICE_ADJUSTMENT;
            restart_timer = TRUE;
-           /* Adjust the age; must be same as in obj_ice_age() */
+           /* Adjust the age; time spent off ice needs to be multiplied
+              by the ice adjustment and subtracted from the age so that
+              later calculations behave as if it had been on ice during
+              that time (longwinded way of saying this is the inverse
+              of removing it from the ice and of peeking at its age). */
            age = monstermoves - otmp->age;
            otmp->age = monstermoves - (age * ROT_ICE_ADJUSTMENT);
        }
@@ -1511,7 +1515,7 @@ int force;        /* 0 = no force so do checks, <0 = force off, >0 force on */
     /* Check for corpses coming off ice */
     else if ((force < 0) ||
             (otmp->otyp == CORPSE && otmp->on_ice &&
-            ((on_floor && !is_ice(x,y)) || !on_floor))) {
+            !((on_floor || buried) && is_ice(x,y)))) {
        tleft = stop_timer(action, obj_to_any(otmp));
        if (tleft == 0L) {
                action = REVIVE_MON;
@@ -1529,7 +1533,7 @@ int force;        /* 0 = no force so do checks, <0 = force off, >0 force on */
                restart_timer = TRUE;
                /* Adjust the age */
                age = monstermoves - otmp->age;
-               otmp->age = otmp->age + (age / ROT_ICE_ADJUSTMENT);
+               otmp->age += age * (ROT_ICE_ADJUSTMENT-1) / ROT_ICE_ADJUSTMENT;
        }
     }
     /* now re-start the timer with the appropriate modifications */