From b530d8b95055c27c737140c5ec2047919d02aeed Mon Sep 17 00:00:00 2001
From: Sverker Eriksson <sverker@erlang.org>
Date: Mon, 26 Jan 2015 17:58:30 +0100
Subject: erts: Add PSTACK

A lightweight stack that can be used to store any type.
PUSH and POP return pointers into stack slots.
---
 erts/emulator/beam/global.h | 61 +++++++++++++++++++++++++++++++++++++++++++++
 erts/emulator/beam/utils.c  | 26 +++++++++++++++++++
 2 files changed, 87 insertions(+)

(limited to 'erts/emulator/beam')

diff --git a/erts/emulator/beam/global.h b/erts/emulator/beam/global.h
index dcba8bbba8..09f43348f4 100644
--- a/erts/emulator/beam/global.h
+++ b/erts/emulator/beam/global.h
@@ -685,6 +685,67 @@ do {						\
 #define WSTACK_POP(s) ((ASSERT(s.wsp > s.wstart)),*(--s.wsp))
 
 
+
+/* PSTACK - Stack of any type.
+ * Usage:
+ * {
+ * #define PSTACK_TYPE MyType
+ *    PSTACK_DECLARE(s,16);
+ *    MyType *sp = PSTACK_PUSH(s);
+ *
+ *    sp->x = ....
+ *    sp->y = ....
+ *    sp = PSTACK_PUSH(s);
+ *    ...
+ *    sp = PSTACK_POP(s);
+ *    if (PSTACK_IS_EMPTY(s)) {
+ *        // sp is invalid when stack is empty after pop
+ *    }
+ *
+ *    PSTACK_DESTROY(s);
+ * }
+ */
+
+
+typedef struct ErtsPStack_ {
+    byte* pstart;
+    byte* psp;
+    byte* pend;
+    ErtsAlcType_t alloc_type;
+}ErtsPStack;
+
+void erl_grow_pstack(ErtsPStack* s, void* default_pstack, unsigned need_bytes);
+#define PSTK_CONCAT(a,b) a##b
+#define PSTK_DEF_STACK(s) PSTK_CONCAT(s,_default_pstack)
+
+#define PSTACK_DECLARE(s, DEF_PSTACK_SIZE) \
+PSTACK_TYPE PSTK_DEF_STACK(s)[DEF_PSTACK_SIZE];                            \
+ErtsPStack s = { (byte*)PSTK_DEF_STACK(s), /* pstart */                    \
+                 (byte*)(PSTK_DEF_STACK(s) - 1), /* psp */                 \
+                 (byte*)(PSTK_DEF_STACK(s) + (DEF_PSTACK_SIZE)), /* pend */\
+                 ERTS_ALC_T_ESTACK   /* alloc_type */                      \
+}
+
+#define PSTACK_DESTROY(s)				\
+do {							\
+    if (s.pstart != (byte*)PSTK_DEF_STACK(s)) {		\
+	erts_free(s.alloc_type, s.pstart); 		\
+    }							\
+} while(0)
+
+#define PSTACK_IS_EMPTY(s) (s.psp < s.pstart)
+
+#define PSTACK_TOP(s) (ASSERT(!PSTACK_IS_EMPTY(s)), (PSTACK_TYPE*)(s.psp))
+
+#define PSTACK_PUSH(s) 		                                           \
+    (s.psp += sizeof(PSTACK_TYPE),                                         \
+     ((s.psp == s.pend) ? erl_grow_pstack(&s, PSTK_DEF_STACK(s),           \
+                                          sizeof(PSTACK_TYPE)) : (void)0), \
+     ((PSTACK_TYPE*) s.psp))
+
+#define PSTACK_POP(s) ((PSTACK_TYPE*) (s.psp -= sizeof(PSTACK_TYPE)))
+
+
 /* binary.c */
 
 void erts_emasculate_writable_binary(ProcBin* pb);
diff --git a/erts/emulator/beam/utils.c b/erts/emulator/beam/utils.c
index bd90ec2fba..a54a93b086 100644
--- a/erts/emulator/beam/utils.c
+++ b/erts/emulator/beam/utils.c
@@ -239,6 +239,32 @@ erl_grow_wstack(ErtsWStack* s, UWord* default_wstack, Uint need)
     s->wsp = s->wstart + sp_offs;
 }
 
+/*
+ * Helper function for the PSTACK macros defined in global.h.
+ */
+void
+erl_grow_pstack(ErtsPStack* s, void* default_pstack, unsigned need_bytes)
+{
+    Uint old_size = s->pend - s->pstart;
+    Uint new_size;
+    Uint sp_offs = s->psp - s->pstart;
+
+    if (need_bytes < old_size)
+	new_size = 2 * old_size;
+    else
+	new_size = ((need_bytes / old_size) + 2) * old_size;
+
+    if (s->pstart != default_pstack) {
+	s->pstart = erts_realloc(s->alloc_type, s->pstart, new_size);
+    } else {
+	byte* new_ptr = erts_alloc(s->alloc_type, new_size);
+	sys_memcpy(new_ptr, s->pstart, old_size);
+	s->pstart = new_ptr;
+    }
+    s->pend = s->pstart + new_size;
+    s->psp = s->pstart + sp_offs;
+}
+
 /* CTYPE macros */
 
 #define LATIN1
-- 
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