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[master] / src / liblimb / base.h / base_fmt.c 

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/* This file is part of limb                           https://lila.oss/limb
 * Copyright (C) 2023 Olivier Brunel                          jjk@jjacky.com */
/* SPDX-License-Identifier: GPL-2.0-only */
#include <errno.h>
#include <string.h>
#include <limb/base.h>
#include <limb/u64.h>

ssize_t
base_fmt(char *dst, int base, const char *data_, size_t dlen, const char *alpha, int strict)
{
    const unsigned char *data = (const unsigned char *) data_;
    size_t bits, bin, bout, msk;
    size_t w = 0;

    switch (base) {
        case   2: bits = 1; bin = 1; bout = 8; break;
        case   4: bits = 2; bin = 1; bout = 4; break;
        case   8: bits = 3; bin = 3; bout = 8; break;
        case  16: bits = 4; bin = 1; bout = 2; break;
        case  32: bits = 5; bin = 5; bout = 8; break;
        case  64: bits = 6; bin = 3; bout = 4; break;
        case 128: bits = 7; bin = 7; bout = 8; break;
        default: return (errno = ERANGE, -1);
    }
    msk = (1 << bits) - 1;

    while (dlen) {
        size_t l, o, pad;
        if (dlen < bin) {
            l = dlen;
            o = bout * l / bin;
            if (bout * l % bin)
                ++o;
            if (strict) pad = bout - o;
            else pad = 1;
        } else {
            l = bin;
            o = bout;
            pad = 0;
        }

        if (dst) {
            u64 u = 0;
            memcpy(&u, data, l);
            u64p_be(&u);

            for (size_t i = 0; i < o; ++i)
                dst[i] = alpha[(u >> (64 - bits * (i + 1))) & msk];
            memset(dst + o, alpha[base], pad);
            o += pad;

            dst += o;
            data += l;
        } else {
            o += pad;
        }

        w += o;
        dlen -= l;
    }

    return w;
}