Better cross-platform handling of time calcs

Thanks to integral promotion, a C compiler might treat the intermediate
value (t1 - t0) as a larger signed value when t1 and t0 are unsigned
values.  Cast the intermediate result to unsigned in these cases, as
this is necessary to get the correct result in the case of timer value
roll-over.

diff --git a/tmr.c b/tmr.c
index 09e6c2d3cef8dbbb1fe0170442bac3c77175bd8e..f07b4b3bbfe15e6af250c8b7fbeff89e5df40bca 100644 (file)
--- a/tmr.c
+++ b/tmr.c
@@ -108,7 +108,8 @@ void tmr_isr()
     TMR0IF = 0;
     _tmr_ticks++;
     for (tmr_bitno_t t = 0; t < TMR_COUNT; t++) {
-      if (bit_get(_tmr_on, t) && _tmr_ticks - _tmr_t0[t] >= _tmr_elapsed[t]) {
+      if (bit_get(_tmr_on, t) &&
+          (tmr_time_t)(_tmr_ticks - _tmr_t0[t]) >= _tmr_elapsed[t]) {
         bit_set(_tmr_flag, t);
         if (bit_get(_tmr_periodic, t))
           _tmr_t0[t] += _tmr_elapsed[t];

diff --git a/tmr.h b/tmr.h
index a204ab000675ed0f362c26465e95c3cc010c0d21..e985e1cfc0aff31be6d4e57510d4c452e3f4d37d 100644 (file)
--- a/tmr.h
+++ b/tmr.h
@@ -98,8 +98,8 @@ void tmr_isr();
 /* Wait for c clocks, 0 <= c < 128. */
 #define tmr_cwait(c) \
   do { \
-    unsigned t0 = TMR0; \
-    while (TMR0 - t0 <= c); \
+    unsigned char t0 = TMR0; \
+    while ((unsigned char)(TMR0 - t0) <= c); \
   } while (0)
 
 /* Wait for a number of us.  This is pretty accurate. */