--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/druntime/src/compiler/dmd/alloca.d	Tue Nov 11 01:52:37 2008 +0100
@@ -0,0 +1,110 @@
+/*_ _alloca.d
+ * Copyright (C) 1990-2003 by Digital Mars, www.digitalmars.com
+ * All Rights Reserved
+ * Written by Walter Bright
+ */
+
+module rt.alloca;
+
+/+
+#if DOS386
+extern size_t _x386_break;
+#else
+extern size_t _pastdata;
+#endif
++/
+
+/*******************************************
+ * Allocate data from the caller's stack frame.
+ * This is a 'magic' function that needs help from the compiler to
+ * work right, do not change its name, do not call it from other compilers.
+ * Input:
+ *      nbytes  number of bytes to allocate
+ *      ECX     address of variable with # of bytes in locals
+ *              This is adjusted upon return to reflect the additional
+ *              size of the stack frame.
+ * Returns:
+ *      EAX     allocated data, null if stack overflows
+ */
+
+extern (C) void* __alloca(int nbytes)
+{
+    asm
+    {
+        naked                   ;
+        mov     EDX,ECX         ;
+        mov     EAX,4[ESP]      ; // get nbytes
+        push    EBX             ;
+        push    EDI             ;
+        push    ESI             ;
+        add     EAX,3           ;
+        and     EAX,0xFFFFFFFC  ; // round up to dword
+        jnz     Abegin          ;
+        mov     EAX,4           ; // allow zero bytes allocation, 0 rounded to dword is 4..
+    Abegin:
+        mov     ESI,EAX         ; // ESI = nbytes
+        neg     EAX             ;
+        add     EAX,ESP         ; // EAX is now what the new ESP will be.
+        jae     Aoverflow       ;
+    }
+    version (Windows)
+    {
+    asm
+    {
+        // We need to be careful about the guard page
+        // Thus, for every 4k page, touch it to cause the OS to load it in.
+        mov     ECX,EAX         ; // ECX is new location for stack
+        mov     EBX,ESI         ; // EBX is size to "grow" stack
+    L1:
+        test    [ECX+EBX],EBX   ; // bring in page
+        sub     EBX,0x1000      ; // next 4K page down
+        jae     L1              ; // if more pages
+        test    [ECX],EBX       ; // bring in last page
+    }
+    }
+    version (DOS386)
+    {
+    asm
+    {
+        // is ESP off bottom?
+        cmp     EAX,_x386_break ;
+        jbe     Aoverflow       ;
+    }
+    }
+    version (Unix)
+    {
+    asm
+    {
+        cmp     EAX,_pastdata   ;
+        jbe     Aoverflow       ; // Unlikely - ~2 Gbytes under UNIX
+    }
+    }
+    asm
+    {
+        // Copy down to [ESP] the temps on the stack.
+        // The number of temps is (EBP - ESP - locals).
+        mov     ECX,EBP         ;
+        sub     ECX,ESP         ;
+        sub     ECX,[EDX]       ; // ECX = number of temps (bytes) to move.
+        add     [EDX],ESI       ; // adjust locals by nbytes for next call to alloca()
+        mov     ESP,EAX         ; // Set up new stack pointer.
+        add     EAX,ECX         ; // Return value = ESP + temps.
+        mov     EDI,ESP         ; // Destination of copy of temps.
+        add     ESI,ESP         ; // Source of copy.
+        shr     ECX,2           ; // ECX to count of dwords in temps
+                                  // Always at least 4 (nbytes, EIP, ESI,and EDI).
+        rep                     ;
+        movsd                   ;
+        jmp     done            ;
+
+    Aoverflow:
+        // Overflowed the stack.  Return null
+        xor     EAX,EAX         ;
+
+    done:
+        pop     ESI             ;
+        pop     EDI             ;
+        pop     EBX             ;
+        ret                     ;
+    }
+}