features.h

// SPDX-FileCopyrightText: 2026 Edward Kmett <ekmett@gmail.com>
// SPDX-License-Identifier: BSD-2-Clause OR Apache-2.0
#pragma once
#include "native/isa.h"
#include <span>
#include <optional>
 
namespace native {
 
  namespace detail {
    // Complete import-free modules; v128.const and i8x16.relaxed_swizzle.
    // The JS bridge carries the same bytes, checked by the consumer tests.
    inline constexpr std::uint8_t wasm_simd128_probe[]{
      0,97,115,109,1,0,0,0, 1,5,1,0x60,0,1,0x7b, 3,2,1,0,
      10,22,1,20,0, 0xfd,0x0c,
      0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0x0b
    };
    inline constexpr std::uint8_t wasm_relaxed_simd_probe[]{
      0,97,115,109,1,0,0,0, 1,7,1,0x60,2,0x7b,0x7b,1,0x7b, 3,2,1,0,
      10,11,1,9,0, 0x20,0,0x20,1,0xfd,0x80,0x02,0x0b
    };
  }

  constexpr std::span<std::uint8_t const> wasm_feature_probe(wasm_feature feature) noexcept {
    switch(feature) {
      case wasm_feature::simd128: return detail::wasm_simd128_probe;
      case wasm_feature::relaxed_simd: return detail::wasm_relaxed_simd_probe;
    }
    return {};
  }

  struct wasm_capabilities {
    isa<wasm> present{};
    isa<wasm> observed{};
    struct raw_observations {
      bool simd128_observed = false;
      bool simd128 = false;
      bool relaxed_simd_observed = false;
      bool relaxed_simd = false;
    };

    raw_observations raw{};
  };

  constexpr wasm_capabilities decode_wasm_capabilities(wasm_capabilities::raw_observations raw) noexcept {
    wasm_capabilities result;
    result.raw=raw;
    result.observed.set(wasm_feature::simd128,raw.simd128_observed);
    result.present.set(wasm_feature::simd128,raw.simd128_observed && raw.simd128);
    result.observed.set(wasm_feature::relaxed_simd,raw.relaxed_simd_observed);
    result.present.set(wasm_feature::relaxed_simd,raw.relaxed_simd_observed && raw.relaxed_simd);
    return result;
  }

  template<class V> requires requires(V & validate,std::span<std::uint8_t const> bytes) {
    { validate(bytes) } noexcept -> std::same_as<std::optional<bool>>;
  }
  constexpr wasm_capabilities observe_wasm_capabilities(V && validate) noexcept {
    auto baseline=validate(wasm_feature_probe(wasm_feature::simd128).first(8));
    if(!baseline || !*baseline) return {};
    auto simd128=validate(wasm_feature_probe(wasm_feature::simd128));
    auto relaxed_simd=validate(wasm_feature_probe(wasm_feature::relaxed_simd));
    return decode_wasm_capabilities({simd128.has_value(),simd128.value_or(false),
      relaxed_simd.has_value(),relaxed_simd.value_or(false)});
  }

  constexpr wasm_capabilities observe_wasm_capabilities() noexcept { return {}; }
}