codegen integer literals correctly

This was not as easy as one would expect ☠️

1 files changed, 26 insertions, 2 deletions

diff --git a/src/lexer.zig b/src/lexer.zig
index 67beec9..8586765 100644
--- a/src/lexer.zig
+++ b/src/lexer.zig
@@ -1,3 +1,5 @@
+const std = @import("std");
+
 pub const Token = struct {
     loc: Location,
     type: Type,
@@ -20,6 +22,16 @@ pub const Location = struct {
         if (a.end > b.start) unreachable;
         return .{ .start = @min(a.start, b.start), .end = @max(a.end, b.end) };
     }
+
+    /// Assumes that the location comes directly from an `integer_literal` token.
+    pub fn getInt(self: Location, file_source: []const u8) u64 {
+        var value: u64 = 0;
+        for (file_source[self.start..self.end]) |c| {
+            std.debug.assert('0' <= c and c <= '9');
+            value = value * 10 + (c - '0');
+        }
+        return value;
+    }
 };
 
 source: []const u8,
@@ -41,10 +53,22 @@ pub fn next(self: *Self) ?Token {
 }
 
 fn integerLiteral(self: *Self) Token {
-    while (digitValue(self.peek()) != null) {
+    var value: ?u64 = 0;
+    while (digitValue(self.peek())) |v| {
+        var nxt: ?u64 = null;
+        if (value) |val|
+            if (std.math.mul(u64, val, 10) catch null) |p|
+                if (std.math.add(u64, p, v) catch null) |s| {
+                    nxt = s;
+                };
+
+        value = nxt;
         _ = self.eat();
     }
-    return self.create(.{ .integer_literal = {} });
+    return if (value != null)
+        self.create(.{ .integer_literal = {} })
+    else
+        self.create(.{ .invalid = {} });
 }
 
 fn create(self: *Self, tajp: Token.Type) Token {