From d001a6f1a0ec23366ab435d7673908f9690a99bb Mon Sep 17 00:00:00 2001
From: Oliver Schmidt <ol.sc@web.de>
Date: Thu, 20 Feb 2014 21:03:52 +0100
Subject: [PATCH] Have _heapmaxavail() work as advertised.

The cc65 doc explicitly states that the return value of _heapmaxavail() can be used as parameter of malloc(). To actually allow for that the size of HEAP_ADMIN_SPACE has to be substracted from the raw size of the largest free heap block.
---
 libsrc/common/_heapmaxavail.s | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/libsrc/common/_heapmaxavail.s b/libsrc/common/_heapmaxavail.s
index 16fc10dde..4d44fadc1 100644
--- a/libsrc/common/_heapmaxavail.s
+++ b/libsrc/common/_heapmaxavail.s
@@ -61,7 +61,7 @@ __heapmaxavail:
 
 ; F = F->next;
 
-@L2:    iny                             ; Points to F->next
+@L2:    iny                     ; Points to F->next
         lda     (ptr1),y
         tax
         iny
@@ -69,8 +69,17 @@ __heapmaxavail:
         stx     ptr1
         jmp     @L1
 
-; return Size;
+; if (Size < HEAP_ADMIN_SPACE) return 0;
 
 @L3:    lda     ptr2
+        sub     #HEAP_ADMIN_SPACE
         ldx     ptr2+1
+        bcs     @L5
+        bne     @L4
+        txa
         rts
+
+; return Size - HEAP_ADMIN_SPACE;
+
+@L4:    dex
+@L5:    rts