#define _POSIX_C_SOURCE 200112L
#include "taps.h"
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

static const short *
find(int n)
{
    for (int i = 0; i < NTAPS; i++)
        if (taps[i * 5] == n)
            return taps + i * 5 + 1;
    return 0;
}

static void
generate_c_ull_shr(int n)
{
    const short *t = find(n);
    int blocks = (n + 63) / 64;
    unsigned long long masks[4096 / 64] = {0};
    for (int i = 0; i < 4; i++) {
        if (t[i]) {
            int b = t[i] - 1;
            masks[b / 64] |= 1ULL << (b % 64);
        }
    }
    printf("#define LFSR%d_TAPS {", n);
    for (int i = 0; i < 4; i++)
        if (t[i])
            printf("%s%d", i ? ", " : "", t[i]);
    printf("}\n");
    printf("static int\nlfsr%d(unsigned long long s[%d])\n{\n", n, blocks);
    printf("    unsigned long long b = s[0] & 1ULL;\n");
    for (int i = 0; i < blocks - 1; i++)
        printf("    s[%d]  = s[%d] >> 1 | s[%d] << 63;\n", i, i, i + 1);
    printf("    s[%d]  = s[%d] >> 1;\n", blocks - 1, blocks - 1);
    for (int i = 0; i < blocks; i++)
        if (masks[i])
            printf("    s[%d] ^= -b & 0x%016llxULL;\n", i, masks[i]);
    printf("    return b;\n}\n");
}

static void
generate_c_ull_shl(int n)
{
    const short *t = find(n);
    int blocks = (n + 63) / 64;
    unsigned long long masks[4096 / 64] = {0};
    for (int i = 0; i < 4; i++) {
        if (t[i]) {
            int b = t[i] - 1;
            masks[b / 64] |= 1ULL << (63 - (b % 64));
        }
    }
    printf("#define LFSR%d_TAPS {", n);
    for (int i = 0; i < 4; i++)
        if (t[i])
            printf("%s%d", i ? ", " : "", t[i]);
    printf("}\n");
    printf("static int\nlfsr%d(unsigned long long s[%d])\n{\n", n, blocks);
    printf("    unsigned long long b = s[0] >> 63;\n");
    for (int i = 0; i < blocks - 1; i++)
        printf("    s[%d]  = s[%d] << 1 | s[%d] >> 63;\n", i, i, i + 1);
    printf("    s[%d]  = s[%d] << 1;\n", blocks - 1, blocks - 1);
    for (int i = 0; i < blocks; i++)
        if (masks[i])
            printf("    s[%d] ^= -b & 0x%016llxULL;\n", i, masks[i]);
    printf("    return b;\n}\n");
}

static void
generate_js(int n)
{
    const short *t = find(n);
    int blocks = (n + 31) / 32;
    unsigned long tbits = n % 32;
    unsigned long masks[4096 / 32] = {0};
    for (int i = 0; i < 4; i++) {
        if (t[i]) {
            int b = t[i] - 1;
            masks[b / 32] |= 1ULL << (b % 32);
        }
    }
    printf("function lfsr%d() {\n", n);
    printf("    let taps = [");
    for (int i = 0; i < 4; i++)
        if (t[i])
            printf("%s%d", i ? ", " : "", t[i]);
    printf("];\n");
    printf("    let s = new Uint32Array(%d);\n", blocks);
    printf("    for (let i = 0; i < %d; i++)\n", tbits ? blocks - 1 : blocks);
    printf("        s[i] = Math.random() * 4294967296;\n" );
    if (tbits)
        printf("    s[%d] = Math.random() * %lu;\n", blocks - 1, 1UL << tbits);
    printf("    function next() {\n");
    printf("        let b = s[0] & 1;\n");
    for (int i = 0; i < blocks - 1; i++)
        printf("        s[%d]  = s[%d] >>> 1 | s[%d] << 31;\n", i, i, i + 1);
    printf("        s[%d]  = s[%d] >>> 1;\n", blocks - 1, blocks - 1);
    for (int i = 0; i < blocks; i++)
        if (masks[i])
            printf("        s[%d] ^= -b & 0x%08lx;\n", i, masks[i]);
    printf("        return b;\n    }\n");
    printf("    function bit(n) {\n");
    printf("        return s[Math.floor(n / 32)] >> (n %% 32) & 1;\n");
    printf("    }\n");
    printf("    return {next: next, bit: bit, n: %d, taps: taps};\n", n);
    printf("}\n");
}

static void
usage(FILE *f)
{
    fprintf(f, "usage: lfsrgen [-hr] [-l LANG] [-n BITS]\n");
    fprintf(f, "  -h          print this message\n");
    fprintf(f, "  -l LANG     output language (c, js)\n");
    fprintf(f, "  -n BITS     LFSR size\n");
    fprintf(f, "  -r          reverse shift\n");
}

int
main(int argc, char *argv[])
{
    int n = 256;
    int option;
    int shift = 'L';
    const char *lang = "c";

    while ((option = getopt(argc, argv, "hl:n:r")) != -1) {
        switch (option) {
            case 'h': {
                usage(stdout);
                exit(EXIT_SUCCESS);
            } break;
            case 'l': {
                lang = optarg;
            } break;
            case 'n': {
                n = atoi(optarg);
            } break;
            case 'r': {
                shift = 'R';
            } break;
            default: {
                usage(stderr);
                exit(EXIT_FAILURE);
            } break;
        }
    }

    if (!find(n)) {
        fprintf(stderr, "lfsrgen: %d bits unsupported\n", n);
        exit(EXIT_FAILURE);
    }
    switch (lang[0]) {
        case 'c':
            switch (shift) {
                case 'R': generate_c_ull_shr(n); break;
                case 'L': generate_c_ull_shl(n); break;
            }
            break;
        case 'j':
            generate_js(n);
            break;
        default:
            fprintf(stderr, "lfsrgen: unknown language -- %s\n", lang);
            exit(EXIT_FAILURE);
            break;
    }
}