/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright 2017 Jason king
 * Copyright 2019, Joyent, Inc.
 */

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/debug.h>
#include "libcmdutils.h"

/* The largest suffix that can fit, aka an exabyte (2^60 / 10^18) */
#define INDEX_MAX       (6)

/* Verify INDEX_MAX fits */
CTASSERT(INDEX_MAX * 10 < sizeof (uint64_t) * 8);

void
nicenum_scale(uint64_t n, size_t units, char *buf, size_t buflen,
    uint32_t flags)
{
        uint64_t divamt = 1024;
        uint64_t divisor = 1;
        int index = 0;
        int rc = 0;
        const char *spc = "";
        char u;

        if (flags & NN_UNIT_SPACE) {
                spc = " ";
        }

        if (units == 0)
                units = 1;

        if (n > 0) {
                n *= units;
                if (n < units)
                        goto overflow;
        }

        if (flags & NN_DIVISOR_1000)
                divamt = 1000;

        /*
         * This tries to find the suffix S(n) such that
         * S(n) <= n < S(n+1), where S(n) = 2^(n*10) | 10^(3*n)
         * (i.e. 1024/1000, 1,048,576/1,000,000, etc).  Stop once S(n)
         * is the largest prefix supported (i.e. don't bother computing
         * and checking S(n+1).  Since INDEX_MAX should be the largest
         * suffix that fits (currently an exabyte), S(INDEX_MAX + 1) is
         * never checked as it would overflow.
         */
        while (index < INDEX_MAX) {
                uint64_t newdiv = divisor * divamt;

                /* CTASSERT() guarantee these never trip */
                VERIFY3U(newdiv, >=, divamt);
                VERIFY3U(newdiv, >=, divisor);

                if (n < newdiv)
                        break;

                divisor = newdiv;
                index++;
        }

        u = " KMGTPE"[index];

        if (index == 0) {
                rc = snprintf(buf, buflen, "%llu%s", n, spc);
        } else if (n % divisor == 0) {
                /*
                 * If this is an even multiple of the base, always display
                 * without any decimal precision.
                 */
                rc = snprintf(buf, buflen, "%llu%s%c", n / divisor, spc, u);
        } else {
                /*
                 * We want to choose a precision that reflects the best choice
                 * for fitting in the buffer.  This can get rather tricky
                 * when we have numbers that are very close to an order of
                 * magnitude.  For example, when displaying 10239 (which is
                 * really 9.999K), we want only a single place of precision
                 * for 10.0K.  We could develop some complex heuristics for
                 * this, but it's much easier just to try each combination
                 * in turn.
                 */
                int i;
                for (i = 2; i >= 0; i--) {
                        if ((rc = snprintf(buf, buflen, "%.*f%s%c", i,
                            (double)n / divisor, spc, u)) <= (buflen - 1))
                                break;
                }
        }

        if (rc + 1 > buflen || rc < 0)
                goto overflow;

        return;

overflow:
        /* prefer a more verbose message if possible */
        if (buflen > 10)
                (void) strlcpy(buf, "<overflow>", buflen);
        else
                (void) strlcpy(buf, "??", buflen);
}

void
nicenum(uint64_t num, char *buf, size_t buflen)
{
        nicenum_scale(num, 1, buf, buflen, 0);
}