1 files changed, 87 insertions, 0 deletions
diff --git a/src/libzisp/value/fixnum.zig b/src/libzisp/value/fixnum.zig
new file mode 100644
index 0000000..60b4239
--- /dev/null
+++ b/src/libzisp/value/fixnum.zig
@@ -0,0 +1,87 @@
+const std = @import("std");
+
+const Value = @import("../value.zig").Value;
+
+// Zig API
+
+/// Checks for a Zisp fixnum.
+pub fn check(v: Value) bool {
+    return v.isPacked() and v.fixnum.is_fixnum;
+}
+
+/// Asserts check().
+pub fn assert(v: Value) void {
+    if (!check(v)) {
+        v.dump();
+        @panic("not fixnum");
+    }
+}
+
+// See detailed NaN packing docs for why the +/- 1.
+const fixnum_min = std.math.minInt(i52) + 1;
+const fixnum_max = std.math.maxInt(i52) - 1;
+
+fn isValidRange(int: i64) bool {
+    return fixnum_min < int and int < fixnum_max;
+}
+
+fn assertValidRange(int: i64) void {
+    if (int < fixnum_min) {
+        std.debug.print("int too small for fixnum: {}", .{int});
+        @panic("int too small for fixnum");
+    }
+    if (int > fixnum_max) {
+        std.debug.print("int too large for fixnum: {}", .{int});
+        @panic("int too large for fixnum");
+    }
+}
+
+fn packNegative(int: i64) Value {
+    return @bitCast(int);
+}
+
+fn unpackNegative(v: Value) i64 {
+    return @bitCast(v);
+}
+
+const positive_mask: u64 = 0xfff7ffffffffffff;
+
+fn packPositive(int: i64) Value {
+    const uint: u64 = @bitCast(int);
+    return @bitCast(uint ^ positive_mask);
+}
+
+fn unpackPositive(v: Value) i64 {
+    const uint: u64 = @bitCast(v);
+    return @bitCast(uint ^ positive_mask);
+}
+
+pub fn pack(int: i64) Value {
+    assertValidRange(int);
+    if (int < 0) {
+        return packNegative(int);
+    } else {
+        return packPositive(int);
+    }
+}
+
+pub fn unpack(v: Value) i64 {
+    assert(v);
+    if (v.fixnum.negative) {
+        return unpackNegative(v);
+    } else {
+        return unpackPositive(v);
+    }
+}
+
+// Zisp API
+
+pub fn pred(v: Value) Value {
+    return Value.boole.pack(check(v));
+}
+
+pub fn add(v1: Value, v2: Value) Value {
+    const int1 = unpack(v1);
+    const int2 = unpack(v2);
+    return pack(int1 + int2);
+}