doubleConstAssumeCapacity

fn doubleConstAssumeCapacity(self: *Builder, val: f64) Constant {
    const Adapter = struct {
        builder: *const Builder,
        pub fn hash(_: @This(), key: f64) u32 {
            return @truncate(std.hash.Wyhash.hash(
                comptime std.hash.int(@backingInt(Constant.Tag.double)),
                std.mem.asBytes(&key),
            ));
        }
        pub fn eql(ctx: @This(), lhs_key: f64, _: void, rhs_index: usize) bool {
            if (ctx.builder.constant_items.items(.tag)[rhs_index] != .double) return false;
            const rhs_data = ctx.builder.constant_items.items(.data)[rhs_index];
            const rhs_extra = ctx.builder.constantExtraData(Constant.Double, rhs_data);
            return @as(u64, @bitCast(lhs_key)) == @as(u64, rhs_extra.hi) << 32 | rhs_extra.lo;
        }
    };
    const gop = self.constant_map.getOrPutAssumeCapacityAdapted(val, Adapter{ .builder = self });
    if (!gop.found_existing) {
        gop.key_ptr.* = {};
        gop.value_ptr.* = {};
        self.constant_items.appendAssumeCapacity(.{
            .tag = .double,
            .data = self.addConstantExtraAssumeCapacity(Constant.Double{
                .lo = @truncate(@as(u64, @bitCast(val))),
                .hi = @intCast(@as(u64, @bitCast(val)) >> 32),
            }),
        });
    }
    return @fromBackingInt(@intCast(gop.index));
}