# HG changeset patch
# User Steve Losh <steve@stevelosh.com>
# Date 1462908789 0
# Node ID 0a4b04d4dfa7fd754446cfe06f3273921f623c1d
# Parent  b073c3d4a7a97331e53670b94a5d4b8699b337b0
Reserve an extra tag bit for the coming optimizations

diff -r b073c3d4a7a9 -r 0a4b04d4dfa7 src/wam/constants.lisp
--- a/src/wam/constants.lisp	Tue May 10 19:05:13 2016 +0000
+++ b/src/wam/constants.lisp	Tue May 10 19:33:09 2016 +0000
@@ -3,13 +3,13 @@
 (define-constant +cell-width+ 16
   :documentation "Number of bits in each cell.")
 
-(define-constant +cell-tag-width+ 2
+(define-constant +cell-tag-width+ 3
   :documentation "Number of bits reserved for cell type tags.")
 
 (define-constant +cell-value-width+ (- +cell-width+ +cell-tag-width+)
   :documentation "Number of bits reserved for cell values.")
 
-(define-constant +cell-tag-bitmask+ #b11
+(define-constant +cell-tag-bitmask+ #b111
   :documentation "Bitmask for masking the cell type tags.")
 
 
@@ -24,18 +24,21 @@
   :documentation "Sentinel value used in the PC and CP.")
 
 
-(define-constant +tag-null+      #b00
+(define-constant +tag-null+      #b000
   :documentation "An empty cell.")
 
-(define-constant +tag-structure+ #b01
+(define-constant +tag-structure+ #b001
   :documentation "A structure cell.")
 
-(define-constant +tag-reference+ #b10
+(define-constant +tag-reference+ #b010
   :documentation "A pointer to a cell.")
 
-(define-constant +tag-functor+   #b11
+(define-constant +tag-functor+   #b011
   :documentation "A functor.")
 
+(define-constant +tag-constant+  #b100
+  :documentation "A constant (i.e. a 0-arity functor).")
+
 
 (define-constant +register-count+ 2048
   :documentation "The number of local registers the WAM has available.")