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authorSamuel Williams <samuel.williams@oriontransfer.co.nz>2019-06-03 09:35:03 (GMT)
committerSamuel Williams <samuel.williams@oriontransfer.co.nz>2019-07-11 23:56:51 (GMT)
commita2adcd40df96acd1218cc60dc1810e83dbc124d8 (patch)
treead4235c8ea1fee82012b2fc59ecebd0824c480b8 /gc.h
parent5c8061a9e2a34df975846d724273cb5be7d74a7c (diff)
Add note about `STACK_GROW_DIR_DETECTION`.
Diffstat (limited to 'gc.h')
-rw-r--r--gc.h8
1 files changed, 8 insertions, 0 deletions
diff --git a/gc.h b/gc.h
index f3b433f..07c0857 100644
--- a/gc.h
+++ b/gc.h
@@ -81,6 +81,14 @@ int ruby_get_stack_grow_direction(volatile VALUE *addr);
# define STACK_UPPER(x, a, b) (stack_growup_p(x) ? (a) : (b))
#endif
+/*
+ STACK_GROW_DIR_DETECTION is used with STACK_DIR_UPPER.
+
+ On most normal systems, stacks grow from high address to lower address. In
+ this case, STACK_DIR_UPPER(a, b) will return (b), but on exotic systems where
+ the stack grows UP (from low address to high address), it will return (a).
+*/
+
#if STACK_GROW_DIRECTION
#define STACK_GROW_DIR_DETECTION
#define STACK_DIR_UPPER(a,b) STACK_UPPER(0, (a), (b))