// Copyright 2017 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.

// TODO: drop the '?' but still generate wuffs_adler32__hasher__initialize?
pub struct hasher? implements base.hasher_u32(
        state   : base.u32,
        started : base.bool,
)

pub func hasher.set_quirk!(key: base.u32, value: base.u64) base.status {
    return base."#unsupported option"
}

pub func hasher.update_u32!(x: roslice base.u8) base.u32 {
    if not this.started {
        this.started = true
        this.state = 1
        // There used to be an up_x86_avx2 implementation too, but while it
        // made the std/adler32 micro-benchmarks better, it also made the
        // std/zlib and std/png micro-benchmarks worse. See commit baec831f
        // "Add std/adler32 hasher.up_x86_avx2".
        choose up = [
                up_arm_neon,
                up_x86_sse42]
    }
    this.up!(x: args.x)
    return this.state
}

pri func hasher.up!(x: roslice base.u8),
        choosy,
{
    // The Adler-32 checksum's magic 65521 and 5552 numbers are discussed in
    // this package's README.md.

    var s1        : base.u32
    var s2        : base.u32
    var remaining : roslice base.u8
    var p         : roslice base.u8

    s1 = this.state.low_bits(n: 16)
    s2 = this.state.high_bits(n: 16)
    while args.x.length() > 0 {
        remaining = args.x[.. 0]
        if args.x.length() > 5552 {
            remaining = args.x[5552 ..]
            args.x = args.x[.. 5552]
        }

        // The SIMD versions of this function replace this simple iterate loop.
        iterate (p = args.x)(length: 1, advance: 1, unroll: 8) {
            s1 ~mod+= p[0] as base.u32
            s2 ~mod+= s1
        }

        s1 %= 65521
        s2 %= 65521
        args.x = remaining
    } endwhile
    this.state = ((s2 & 0xFFFF) << 16) | (s1 & 0xFFFF)
}