// SPDX-License-Identifier: GPL-2.0-only
/* -*- linux-c -*- ------------------------------------------------------- *
 *
 *   Copyright (C) 1991, 1992 Linus Torvalds
 *   Copyright 2007 rPath, Inc. - All Rights Reserved
 *
 * ----------------------------------------------------------------------- */

/*
 * Oh, it's a waste of space, but oh-so-yummy for debugging.
 */

#include <linux/stdarg.h>

#include <linux/compiler.h>
#include <linux/ctype.h>
#include <linux/kernel.h>
#include <linux/limits.h>
#include <linux/string.h>
#include <linux/types.h>

static
int skip_atoi(const char **s)
{
        int i = 0;

        while (isdigit(**s))
                i = i * 10 + *((*s)++) - '0';
        return i;
}

/*
 * put_dec_full4 handles numbers in the range 0 <= r < 10000.
 * The multiplier 0xccd is round(2^15/10), and the approximation
 * r/10 == (r * 0xccd) >> 15 is exact for all r < 16389.
 */
static
void put_dec_full4(char *end, unsigned int r)
{
        int i;

        for (i = 0; i < 3; i++) {
                unsigned int q = (r * 0xccd) >> 15;
                *--end = '0' + (r - q * 10);
                r = q;
        }
        *--end = '0' + r;
}

/* put_dec is copied from lib/vsprintf.c with small modifications */

/*
 * Call put_dec_full4 on x % 10000, return x / 10000.
 * The approximation x/10000 == (x * 0x346DC5D7) >> 43
 * holds for all x < 1,128,869,999.  The largest value this
 * helper will ever be asked to convert is 1,125,520,955.
 * (second call in the put_dec code, assuming n is all-ones).
 */
static
unsigned int put_dec_helper4(char *end, unsigned int x)
{
        unsigned int q = (x * 0x346DC5D7ULL) >> 43;

        put_dec_full4(end, x - q * 10000);
        return q;
}

/* Based on code by Douglas W. Jones found at
 * <http://www.cs.uiowa.edu/~jones/bcd/decimal.html#sixtyfour>
 * (with permission from the author).
 * Performs no 64-bit division and hence should be fast on 32-bit machines.
 */
static
char *put_dec(char *end, unsigned long long n)
{
        unsigned int d3, d2, d1, q, h;
        char *p = end;

        d1  = ((unsigned int)n >> 16); /* implicit "& 0xffff" */
        h   = (n >> 32);
        d2  = (h      ) & 0xffff;
        d3  = (h >> 16); /* implicit "& 0xffff" */

        /* n = 2^48 d3 + 2^32 d2 + 2^16 d1 + d0
             = 281_4749_7671_0656 d3 + 42_9496_7296 d2 + 6_5536 d1 + d0 */
        q = 656 * d3 + 7296 * d2 + 5536 * d1 + ((unsigned int)n & 0xffff);
        q = put_dec_helper4(p, q);
        p -= 4;

        q += 7671 * d3 + 9496 * d2 + 6 * d1;
        q = put_dec_helper4(p, q);
        p -= 4;

        q += 4749 * d3 + 42 * d2;
        q = put_dec_helper4(p, q);
        p -= 4;

        q += 281 * d3;
        q = put_dec_helper4(p, q);
        p -= 4;

        put_dec_full4(p, q);
        p -= 4;

        /* strip off the extra 0's we printed */
        while (p < end && *p == '0')
                ++p;

        return p;
}

static
char *number(char *end, unsigned long long num, int base, char locase)
{
        /*
         * locase = 0 or 0x20. ORing digits or letters with 'locase'
         * produces same digits or (maybe lowercased) letters
         */

        /* we are called with base 8, 10 or 16, only, thus don't need "G..."  */
        static const char digits[16] = "0123456789ABCDEF"; /* "GHIJKLMNOPQRSTUVWXYZ"; */

        switch (base) {
        case 10:
                if (num != 0)
                        end = put_dec(end, num);
                break;
        case 8:
                for (; num != 0; num >>= 3)
                        *--end = '0' + (num & 07);
                break;
        case 16:
                for (; num != 0; num >>= 4)
                        *--end = digits[num & 0xf] | locase;
                break;
        default:
                unreachable();
        }

        return end;
}

#define ZEROPAD 1               /* pad with zero */
#define SIGN    2               /* unsigned/signed long */
#define PLUS    4               /* show plus */
#define SPACE   8               /* space if plus */
#define LEFT    16              /* left justified */
#define SMALL   32              /* Must be 32 == 0x20 */
#define SPECIAL 64              /* 0x */
#define WIDE    128             /* UTF-16 string */

static
int get_flags(const char **fmt)
{
        int flags = 0;

        do {
                switch (**fmt) {
                case '-':
                        flags |= LEFT;
                        break;
                case '+':
                        flags |= PLUS;
                        break;
                case ' ':
                        flags |= SPACE;
                        break;
                case '#':
                        flags |= SPECIAL;
                        break;
                case '0':
                        flags |= ZEROPAD;
                        break;
                default:
                        return flags;
                }
                ++(*fmt);
        } while (1);
}

static
int get_int(const char **fmt, va_list *ap)
{
        if (isdigit(**fmt))
                return skip_atoi(fmt);
        if (**fmt == '*') {
                ++(*fmt);
                /* it's the next argument */
                return va_arg(*ap, int);
        }
        return 0;
}

static
unsigned long long get_number(int sign, int qualifier, va_list *ap)
{
        if (sign) {
                switch (qualifier) {
                case 'L':
                        return va_arg(*ap, long long);
                case 'l':
                        return va_arg(*ap, long);
                case 'h':
                        return (short)va_arg(*ap, int);
                case 'H':
                        return (signed char)va_arg(*ap, int);
                default:
                        return va_arg(*ap, int);
                };
        } else {
                switch (qualifier) {
                case 'L':
                        return va_arg(*ap, unsigned long long);
                case 'l':
                        return va_arg(*ap, unsigned long);
                case 'h':
                        return (unsigned short)va_arg(*ap, int);
                case 'H':
                        return (unsigned char)va_arg(*ap, int);
                default:
                        return va_arg(*ap, unsigned int);
                }
        }
}

static
char get_sign(long long *num, int flags)
{
        if (!(flags & SIGN))
                return 0;
        if (*num < 0) {
                *num = -(*num);
                return '-';
        }
        if (flags & PLUS)
                return '+';
        if (flags & SPACE)
                return ' ';
        return 0;
}

static
size_t utf16s_utf8nlen(const u16 *s16, size_t maxlen)
{
        size_t len, clen;

        for (len = 0; len < maxlen && *s16; len += clen) {
                u16 c0 = *s16++;

                /* First, get the length for a BMP character */
                clen = 1 + (c0 >= 0x80) + (c0 >= 0x800);
                if (len + clen > maxlen)
                        break;
                /*
                 * If this is a high surrogate, and we're already at maxlen, we
                 * can't include the character if it's a valid surrogate pair.
                 * Avoid accessing one extra word just to check if it's valid
                 * or not.
                 */
                if ((c0 & 0xfc00) == 0xd800) {
                        if (len + clen == maxlen)
                                break;
                        if ((*s16 & 0xfc00) == 0xdc00) {
                                ++s16;
                                ++clen;
                        }
                }
        }

        return len;
}

static
u32 utf16_to_utf32(const u16 **s16)
{
        u16 c0, c1;

        c0 = *(*s16)++;
        /* not a surrogate */
        if ((c0 & 0xf800) != 0xd800)
                return c0;
        /* invalid: low surrogate instead of high */
        if (c0 & 0x0400)
                return 0xfffd;
        c1 = **s16;
        /* invalid: missing low surrogate */
        if ((c1 & 0xfc00) != 0xdc00)
                return 0xfffd;
        /* valid surrogate pair */
        ++(*s16);
        return (0x10000 - (0xd800 << 10) - 0xdc00) + (c0 << 10) + c1;
}

#define PUTC(c) \
do {                            \
        if (pos < size)         \
                buf[pos] = (c); \
        ++pos;                  \
} while (0);

int vsnprintf(char *buf, size_t size, const char *fmt, va_list ap)
{
        /* The maximum space required is to print a 64-bit number in octal */
        char tmp[(sizeof(unsigned long long) * 8 + 2) / 3];
        char *tmp_end = &tmp[ARRAY_SIZE(tmp)];
        long long num;
        int base;
        const char *s;
        size_t len, pos;
        char sign;

        int flags;              /* flags to number() */

        int field_width;        /* width of output field */
        int precision;          /* min. # of digits for integers; max
                                   number of chars for from string */
        int qualifier;          /* 'h', 'hh', 'l' or 'll' for integer fields */

        va_list args;

        /*
         * We want to pass our input va_list to helper functions by reference,
         * but there's an annoying edge case. If va_list was originally passed
         * to us by value, we could just pass &ap down to the helpers. This is
         * the case on, for example, X86_32.
         * However, on X86_64 (and possibly others), va_list is actually a
         * size-1 array containing a structure. Our function parameter ap has
         * decayed from T[1] to T*, and &ap has type T** rather than T(*)[1],
         * which is what will be expected by a function taking a va_list *
         * parameter.
         * One standard way to solve this mess is by creating a copy in a local
         * variable of type va_list and then passing a pointer to that local
         * copy instead, which is what we do here.
         */
        va_copy(args, ap);

        for (pos = 0; *fmt; ++fmt) {
                if (*fmt != '%' || *++fmt == '%') {
                        PUTC(*fmt);
                        continue;
                }

                /* process flags */
                flags = get_flags(&fmt);

                /* get field width */
                field_width = get_int(&fmt, &args);
                if (field_width < 0) {
                        field_width = -field_width;
                        flags |= LEFT;
                }

                if (flags & LEFT)
                        flags &= ~ZEROPAD;

                /* get the precision */
                precision = -1;
                if (*fmt == '.') {
                        ++fmt;
                        precision = get_int(&fmt, &args);
                        if (precision >= 0)
                                flags &= ~ZEROPAD;
                }

                /* get the conversion qualifier */
                qualifier = -1;
                if (*fmt == 'h' || *fmt == 'l') {
                        qualifier = *fmt;
                        ++fmt;
                        if (qualifier == *fmt) {
                                qualifier -= 'a'-'A';
                                ++fmt;
                        }
                }

                sign = 0;

                switch (*fmt) {
                case 'c':
                        flags &= LEFT;
                        s = tmp;
                        if (qualifier == 'l') {
                                ((u16 *)tmp)[0] = (u16)va_arg(args, unsigned int);
                                ((u16 *)tmp)[1] = L'\0';
                                precision = INT_MAX;
                                goto wstring;
                        } else {
                                tmp[0] = (unsigned char)va_arg(args, int);
                                precision = len = 1;
                        }
                        goto output;

                case 's':
                        flags &= LEFT;
                        if (precision < 0)
                                precision = INT_MAX;
                        s = va_arg(args, void *);
                        if (!s)
                                s = precision < 6 ? "" : "(null)";
                        else if (qualifier == 'l') {
                wstring:
                                flags |= WIDE;
                                precision = len = utf16s_utf8nlen((const u16 *)s, precision);
                                goto output;
                        }
                        precision = len = strnlen(s, precision);
                        goto output;

                        /* integer number formats - set up the flags and "break" */
                case 'o':
                        base = 8;
                        break;

                case 'p':
                        if (precision < 0)
                                precision = 2 * sizeof(void *);
                        fallthrough;
                case 'x':
                        flags |= SMALL;
                        fallthrough;
                case 'X':
                        base = 16;
                        break;

                case 'd':
                case 'i':
                        flags |= SIGN;
                        fallthrough;
                case 'u':
                        flags &= ~SPECIAL;
                        base = 10;
                        break;

                default:
                        /*
                         * Bail out if the conversion specifier is invalid.
                         * There's probably a typo in the format string and the
                         * remaining specifiers are unlikely to match up with
                         * the arguments.
                         */
                        goto fail;
                }
                if (*fmt == 'p') {
                        num = (unsigned long)va_arg(args, void *);
                } else {
                        num = get_number(flags & SIGN, qualifier, &args);
                }

                sign = get_sign(&num, flags);
                if (sign)
                        --field_width;

                s = number(tmp_end, num, base, flags & SMALL);
                len = tmp_end - s;
                /* default precision is 1 */
                if (precision < 0)
                        precision = 1;
                /* precision is minimum number of digits to print */
                if (precision < len)
                        precision = len;
                if (flags & SPECIAL) {
                        /*
                         * For octal, a leading 0 is printed only if necessary,
                         * i.e. if it's not already there because of the
                         * precision.
                         */
                        if (base == 8 && precision == len)
                                ++precision;
                        /*
                         * For hexadecimal, the leading 0x is skipped if the
                         * output is empty, i.e. both the number and the
                         * precision are 0.
                         */
                        if (base == 16 && precision > 0)
                                field_width -= 2;
                        else
                                flags &= ~SPECIAL;
                }
                /*
                 * For zero padding, increase the precision to fill the field
                 * width.
                 */
                if ((flags & ZEROPAD) && field_width > precision)
                        precision = field_width;

output:
                /* Calculate the padding necessary */
                field_width -= precision;
                /* Leading padding with ' ' */
                if (!(flags & LEFT))
                        while (field_width-- > 0)
                                PUTC(' ');
                /* sign */
                if (sign)
                        PUTC(sign);
                /* 0x/0X for hexadecimal */
                if (flags & SPECIAL) {
                        PUTC('0');
                        PUTC( 'X' | (flags & SMALL));
                }
                /* Zero padding and excess precision */
                while (precision-- > len)
                        PUTC('0');
                /* Actual output */
                if (flags & WIDE) {
                        const u16 *ws = (const u16 *)s;

                        while (len-- > 0) {
                                u32 c32 = utf16_to_utf32(&ws);
                                u8 *s8;
                                size_t clen;

                                if (c32 < 0x80) {
                                        PUTC(c32);
                                        continue;
                                }

                                /* Number of trailing octets */
                                clen = 1 + (c32 >= 0x800) + (c32 >= 0x10000);

                                len -= clen;
                                s8 = (u8 *)&buf[pos];

                                /* Avoid writing partial character */
                                PUTC('\0');
                                pos += clen;
                                if (pos >= size)
                                        continue;

                                /* Set high bits of leading octet */
                                *s8 = (0xf00 >> 1) >> clen;
                                /* Write trailing octets in reverse order */
                                for (s8 += clen; clen; --clen, c32 >>= 6)
                                        *s8-- = 0x80 | (c32 & 0x3f);
                                /* Set low bits of leading octet */
                                *s8 |= c32;
                        }
                } else {
                        while (len-- > 0)
                                PUTC(*s++);
                }
                /* Trailing padding with ' ' */
                while (field_width-- > 0)
                        PUTC(' ');
        }
fail:
        va_end(args);

        if (size)
                buf[min(pos, size-1)] = '\0';

        return pos;
}

int snprintf(char *buf, size_t size, const char *fmt, ...)
{
        va_list args;
        int i;

        va_start(args, fmt);
        i = vsnprintf(buf, size, fmt, args);
        va_end(args);
        return i;
}