hello-wuffs-c/parse.wuffs

// Copyright 2019 The Wuffs Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

pri status "#not a digit"
pri status "#too large"

pub struct parser?(
	val : base.u32,
)

pub func parser.parse?(src: base.io_reader) {
	var c : base.u8
	while true {
		c = args.src.read_u8?()
		if c == 0 {
			return ok
		}
		if (c < 0x30) or (0x39 < c) {  // '0' and '9' are ASCII 0x30 and 0x39.
			return "#not a digit"
		}
		// Rebase from ASCII (0x30 ..= 0x39) to the value (0 ..= 9).
		c -= 0x30

		if this.val < 429_496729 {
			this.val = (10 * this.val) + (c as base.u32)
			continue
		} else if (this.val > 429_496729) or (c > 5) {
			return "#too large"
		}
		// Uncomment this assertion to see what facts are known here.
		// assert false
		this.val = (10 * this.val) + (c as base.u32)
	} endwhile
}

pub func parser.value() base.u32 {
	return this.val
}