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Source code

const std = @import("std");

export fn isHelloWorld(str: [*]const u8, len: usize) bool {
    return staticEql("Hello, World!\n", str[0..len]);
}

fn staticEql(comptime a: []const u8, b: []const u8) bool {
    const block_len = std.simd.suggestVectorLength(u8) orelse @sizeOf(usize);

// Exit early if the string lengths don't match up
    if (a.len != b.len) return false;

// Find out how many large "blocks" we can compare at a time
    const block_count = a.len / block_len;
    // Find out how many extra bytes we need to compare
    const rem_count = a.len % block_len;

// Compare "block_len" bytes of text at a time
    for (0..block_count) |idx| {
        const Chunk = std.meta.Int(.unsigned, block_len * 8);
        const a_chunk: Chunk = @bitCast(a[idx * block_len ..][0..block_len].*);
        const b_chunk: Chunk = @bitCast(b[idx * block_len ..][0..block_len].*);
        if (a_chunk != b_chunk) return false;
    }

// Compare the remainder of bytes in both strings
    const Rem = std.meta.Int(.unsigned, rem_count * 8);
    const a_rem: Rem = @bitCast(a[block_count * block_len ..][0..rem_count].*);
    const b_rem: Rem = @bitCast(b[block_count * block_len ..][0..rem_count].*);
    return a_rem == b_rem;
}