X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fcompiler%2Fgeneric%2Fearly-vm.lisp;h=304637d53fb390fe70418b6f410c83be6341cf7e;hb=74cf7a4d01664fbf72a662ba093ad67ca243b524;hp=897d830eb8464c19a4dc967690c6529b1174eef8;hpb=fb15ad0ff2373a50b3b0717f705c49339b39f996;p=sbcl.git

diff --git a/src/compiler/generic/early-vm.lisp b/src/compiler/generic/early-vm.lisp
index 897d830..304637d 100644
--- a/src/compiler/generic/early-vm.lisp
+++ b/src/compiler/generic/early-vm.lisp
@@ -19,11 +19,30 @@
 ;;; pointer
 (def!constant lowtag-limit (ash 1 n-lowtag-bits))
 ;;; the number of tag bits used for a fixnum
-(def!constant n-fixnum-tag-bits (1- n-lowtag-bits))
+(def!constant n-fixnum-tag-bits
+    (if (= 64 sb!vm:n-word-bits)
+        ;; On 64-bit targets, this may be as low as 1 (for 63-bit
+        ;; fixnums) and as high as 3 (for 61-bit fixnums).  The
+        ;; constraint on the low end is that we need at least one bit
+        ;; to determine if a value is a fixnum or not, and the
+        ;; constraint on the high end is that it must not exceed
+        ;; WORD-SHIFT (defined below) due to the use of unboxed
+        ;; word-aligned byte pointers as boxed values in various
+        ;; places.  FIXME: This should possibly be exposed for
+        ;; configuration via customize-target-features.
+        1
+        ;; On 32-bit targets, this may be as low as 2 (for 30-bit
+        ;; fixnums) and as high as 2 (for 30-bit fixnums).  The
+        ;; constraint on the low end is simple overcrowding of the
+        ;; lowtag space, and the constraint on the high end is that it
+        ;; must not exceed WORD-SHIFT.
+        (1- n-lowtag-bits)))
 ;;; the fixnum tag mask
 (def!constant fixnum-tag-mask (1- (ash 1 n-fixnum-tag-bits)))
+;;; the bit width of fixnums
+(def!constant n-fixnum-bits (- n-word-bits n-fixnum-tag-bits))
 ;;; the bit width of positive fixnums
-(def!constant n-positive-fixnum-bits (- n-word-bits n-fixnum-tag-bits 1))
+(def!constant n-positive-fixnum-bits (1- n-fixnum-bits))
 
 ;;; the number of bits to shift between word addresses and byte addresses
 (def!constant word-shift (1- (integer-length (/ n-word-bits n-byte-bits))))
@@ -38,11 +57,11 @@
 (def!constant widetag-mask (1- (ash 1 n-widetag-bits)))
 
 (def!constant sb!xc:most-positive-fixnum
-    (1- (ash 1 (- n-word-bits n-lowtag-bits)))
+    (1- (ash 1 n-positive-fixnum-bits))
   #!+sb-doc
   "the fixnum closest in value to positive infinity")
 (def!constant sb!xc:most-negative-fixnum
-    (ash -1 (- n-word-bits n-lowtag-bits))
+    (ash -1 n-positive-fixnum-bits)
   #!+sb-doc
   "the fixnum closest in value to negative infinity")