From c50f5cd58337e96609479484c2cfd7fcd80db182 Mon Sep 17 00:00:00 2001
From: dos-reis <gdr@axiomatics.org>
Date: Sun, 17 Aug 2014 09:15:57 +0000
Subject: OpenAxiom::VM::Fixnum is now a distinct type.

---
 src/include/vm.H   | 19 +++++++++++--------
 src/rt/Database.cc |  5 +++--
 src/rt/Lisp.cc     | 14 +++++++-------
 src/rt/vm.cc       |  4 ++--
 4 files changed, 23 insertions(+), 19 deletions(-)

(limited to 'src')

diff --git a/src/include/vm.H b/src/include/vm.H
index d386e4c3..0ef6f973 100644
--- a/src/include/vm.H
+++ b/src/include/vm.H
@@ -166,25 +166,28 @@ namespace OpenAxiom {
       // VM integers are divided into classes: small numbers,
       // and large numbers.  A small number fits entirely in a register.
       // A large number is allocated and represented by its address.
-      using Fixnum = intptr_t;
+      using FixnumBits = intptr_t;
+      enum class Fixnum : FixnumBits {
+         minimum = FixnumBits(~(~ValueBits() >> 2)),
+         zero = FixnumBits(0),
+         one = FixnumBits(1),
+         maximum = FixnumBits(~ValueBits() >> 2),
+      };
 
       constexpr ValueBits fix_tag = 0x1;
 
       constexpr bool is_fixnum(Value v) {
-         return (v & 0x1) == fix_tag;
+         return (ValueBits(v) & 0x1) == fix_tag;
       }
 
       constexpr Fixnum to_fixnum(Value v) {
-         return Fixnum(v >> 1);
+         return Fixnum(FixnumBits(v) >> 1);
       }
 
       constexpr Value from_fixnum(Fixnum i) {
-         return (Fixnum(i) << 1 ) | fix_tag;
+         return (ValueBits(i) << 1 ) | fix_tag;
       }
 
-      constexpr Fixnum fixnum_maximum = to_fixnum(~Value{ });
-      constexpr Fixnum fixnum_minimum = -fixnum_maximum - 1;
-
       // ------------
       // -- String --
       // ------------
@@ -262,7 +265,7 @@ namespace OpenAxiom {
       inline Fixnum count_nodes(Value v) {
          if (auto p = to_pair_if_can(v))
             return count_nodes(p);
-         return 0;
+         return Fixnum::zero;
       }
 
       // ---------------
diff --git a/src/rt/Database.cc b/src/rt/Database.cc
index ee620711..df6ec0a3 100644
--- a/src/rt/Database.cc
+++ b/src/rt/Database.cc
@@ -1,4 +1,4 @@
-// Copyright (C) 2013, Gabriel Dos Reis.
+// Copyright (C) 2013-2014, Gabriel Dos Reis.
 // All rights reserved.
 // Written by Gabriel Dos Reis.
 //
@@ -47,7 +47,8 @@ namespace OpenAxiom {
             auto x = reader.read();
             auto offset = Lisp::retract_to_fixnum
                (Lisp::retract_to_pair(ctx.make_value(x))->head);
-            reader.position(offset);
+            auto n = FixnumBits(offset);
+            reader.position(n);
             toc = Lisp::retract_to_pair(ctx.make_value(reader.read()));
          }
          else if (auto data = Lisp::assoc(key, toc))
diff --git a/src/rt/Lisp.cc b/src/rt/Lisp.cc
index 12684181..6f125bf7 100644
--- a/src/rt/Lisp.cc
+++ b/src/rt/Lisp.cc
@@ -77,17 +77,17 @@ namespace OpenAxiom {
       integer_too_large(const Sexpr::IntegerSyntax& x) {
          std::string s { x.lexeme().begin(), x.lexeme().end() };
          throw IntegerOverflow{ s + " is too large for Fixnum; max value is "
-               + std::to_string(fixnum_maximum) };
+               + std::to_string(FixnumBits(Fixnum::maximum)) };
       }
 
-      constexpr auto fixmax_by_ten = fixnum_maximum / 10;
-      constexpr auto fixmax_lsd = fixnum_maximum % 10;
+      constexpr auto fixmax_by_ten = FixnumBits(Fixnum::maximum) / 10;
+      constexpr auto fixmax_lsd = FixnumBits(Fixnum::maximum) % 10;
 
       static Value
       construct(Evaluator* ctx, const Sexpr::IntegerSyntax& x) {
          bool neg = false;
          auto cur = x.lexeme().begin();
-         Fixnum val = 0;
+         FixnumBits val = 0;
          switch (*cur) {
          case '-': neg = true;
          case '+': ++cur;
@@ -102,12 +102,12 @@ namespace OpenAxiom {
                   val = 10 * val + d;
             }
             if (neg) {
-               if (val > fixnum_maximum)
+               if (val > FixnumBits(Fixnum::maximum))
                   integer_too_large(x);
                val = -val;
             }
          }
-         return VM::from_fixnum(val);
+         return VM::from_fixnum(Fixnum(val));
       }
 
       static Value
@@ -250,7 +250,7 @@ namespace OpenAxiom {
          if (v == nil)
             os << "NIL";
          else if (is_fixnum(v))
-            os << to_fixnum(v);
+            os << FixnumBits(to_fixnum(v));
          else if (auto p = to_pair_if_can(v))
             format(p, os);
          else if (auto s = to_string_if_can(v))
diff --git a/src/rt/vm.cc b/src/rt/vm.cc
index 2fe4da1c..a0f4f2e3 100644
--- a/src/rt/vm.cc
+++ b/src/rt/vm.cc
@@ -44,10 +44,10 @@ namespace OpenAxiom {
 
       Fixnum
       count_nodes(Pair p) {
-         Fixnum n = 1;
+         FixnumBits n = 1;
          for (; auto q = to_pair_if_can(p->tail); p = q)
             ++n;
-         return n;
+         return Fixnum(n);
       }
 
       // -- BasicContext --
-- 
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