X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fcompiler%2Fgeneric%2Fearly-vm.lisp;h=304637d53fb390fe70418b6f410c83be6341cf7e;hb=c712f88b26cd7547ee984b90e18c134401335bc3;hp=8810860c7f55a45afd3e3fa89f4fe6e976c70c9b;hpb=dd04bd449535e9016b5652a708a3cac2ca24c87d;p=sbcl.git diff --git a/src/compiler/generic/early-vm.lisp b/src/compiler/generic/early-vm.lisp index 8810860..304637d 100644 --- a/src/compiler/generic/early-vm.lisp +++ b/src/compiler/generic/early-vm.lisp @@ -19,7 +19,24 @@ ;;; 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