embfmt/embformat.c

/* (C) Wiesner András, 2022 */

#include "embformat.h"

#include <stdarg.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>

#define MAX(x, y) (((x) > (y)) ? (x) : (y))
#define MIN(x, y) (((x) < (y)) ? (x) : (y))

#define FORMAT_DELIMITER ('%')

// format length ((nothing),l)
typedef enum {
    LEN_NORMAL, LEN_LONG
} FmtLength;

// format flags ((nothing),0)
typedef enum {
    FLAG_NO = 0, FLAG_LEADING_ZEROS = 1, FLAG_LEADING_SPACES = 2, FLAG_PREPEND_PLUS_SIGN = 4
} FmtFlags;

// format type
typedef enum {
    UNKNOWN = -1, LITERAL_PERCENT, SIGNED_INTEGER, UNSIGNED_INTEGER, DOUBLE, DOUBLE_EXPONENTIAL, UNSIGNED_HEXADECIMAL_INT, UNSIGNED_HEXADECIMAL_INT_UPPERCASE, STRING, CHARACTER
} FmtType;

struct _FmtWord;

typedef int (*printfn)(va_list *va, struct _FmtWord *fmt, char *outbuf, size_t free_space);

// pair of type and designator character
typedef struct {
    char designator;
    FmtType type;
    printfn fn;
} FmtTypeDesignatorPair;

// structure holding format word properties
typedef struct _FmtWord {
    FmtFlags flags;
    int width;
    int precision;
    FmtLength length;
    FmtType type;
    FmtTypeDesignatorPair *pTypeDes;
} FmtWord;

// ---------------------------------------------

// copy a maximum of n characters AND insert '\0' into dst as the n+1-th character
static int string_copy(char *dst, const char *src, size_t n) {
    size_t i;
    int cnt = 0;
    for (i = 0; i < n && src[i] != '\0'; i++) {
        dst[i] = src[i];
        cnt++;
    }
    dst[i] = '\0';
    return cnt;
}

// get the length of a string
static size_t string_length(char *str) {
    size_t len = 0;
    while (*str != '\0') {
        len++;
        str++;
    }
    return len;
}

// calculate power
static uint64_t power(uint64_t a, unsigned long int n) {
    if (n == 0) {
        return 1;
    }
    uint64_t a_orig = a;
    for (unsigned long int i = 0; i < n - 1; i++) {
        a *= a_orig;
    }
    return a;
}

// round to closest base^1 value
static uint64_t round_to_base(uint64_t a, uint64_t base) {
    uint64_t mod = a % base;
    if (2 * mod < base) { // avoid floating-point arithemtics!
        return a - mod;
    } else {
        return a + (base - mod);
    }
}

// ---------------------------------------------

// insert leading characters
// str: inout string
// n_str: length of the input string (NOT buflen, stringlen)
// c: character to be used for filling
// n_insert: number of character to insert
static void insert_leading_characters(char *str, size_t n_str, char c, size_t n_insert) {
    size_t len = string_length(str);
    for (size_t i = 0; i < len; i++) {
        str[len - 1 + n_insert - i] = str[len - i - 1];
    }
    for (size_t i = 0; i < n_insert; i++) {
        str[i] = c;
    }
    str[len + n_insert] = '\0';
}

// get exponent in the scientific form of the input number (i. e. get the highest decimal place)
// l: input number
// base: base
// gntpd: greatest non-zero ten-power divisor
// return: exponent, if l != 0, -1 if l == 0
static int scientific_form_exponent(uint64_t l, unsigned int base, uint64_t *gntpd) {
    int e = -1;
    *gntpd = 1;
    while (l != 0) {
        l /= base;
        *gntpd *= base;
        e++;
    }
    if (*gntpd > 1) {
        (*gntpd) /= base;
    }
    return MAX(e, 0);
}

static int pfn_literal_percent(va_list *va, FmtWord *fmt, char *outbuf, size_t free_space) {
    if (free_space >= 1) {
        outbuf[0] = '%';
        outbuf[1] = '\0';
    }
    return 1;
}

#define INT_PRINT_OUTBUF_SIZE (47)

static char sNumChars[] = "0123456789abcdefABCDEF";

static int print_number(uint64_t u, bool negative, FmtWord *fmt, char *outbuf, size_t free_space) {
    // output buffer fitting the full long int range
    char outstrbuf[INT_PRINT_OUTBUF_SIZE + 1];
    outstrbuf[0] = '\0';
    char *outstr = outstrbuf;

    // separate sign, process only non-negative numbers
    bool sign_prepended = false;
    if (negative) {
        *outstr = '-';
        outstr++;
        sign_prepended = true;
    } else if (fmt->flags & FLAG_PREPEND_PLUS_SIGN) {
        *outstr = '+';
        outstr++;
        sign_prepended = true;
    }

    // base of the numeral system
    int base = 10; // for safety...
    if (fmt->type == UNSIGNED_INTEGER || fmt->type == SIGNED_INTEGER) {
        base = 10;
    } else if (fmt->type == UNSIGNED_HEXADECIMAL_INT || fmt->type == UNSIGNED_HEXADECIMAL_INT_UPPERCASE) {
        base = 16;
    }

    // get number of digits the number consists of
    uint64_t gntpd;
    int digits = scientific_form_exponent(u, base, &gntpd) + 1;

    // convert int to string
    while (gntpd > 0) {
        uint64_t place_value = (u / gntpd); // integer division!
        u -= place_value * gntpd; // substract value corresponding to the place

        if (fmt->type == UNSIGNED_HEXADECIMAL_INT_UPPERCASE && place_value > 9) {
            place_value += 6;
        }
        *outstr = sNumChars[place_value]; // print place value string

        gntpd /= base; // divide by the base (advance to lower place)
        outstr++; // advance in the string
        *outstr = '\0'; // move the terminating zero
    }

    // pad with zeros if requested
    if (fmt->width != -1 && (fmt->flags & FLAG_LEADING_ZEROS || fmt->flags & FLAG_LEADING_SPACES)) {
        int pad_n = MAX(fmt->width - digits - sign_prepended, 0);
        if (pad_n > 0) {
            // pad differently based on padding character
            if (fmt->flags & FLAG_LEADING_ZEROS) { // -00000nnn
                insert_leading_characters(outstrbuf + sign_prepended, INT_PRINT_OUTBUF_SIZE - sign_prepended, '0', pad_n); // insert leading characters
            } else if (fmt->flags & FLAG_LEADING_SPACES) { // _____-nnn
                insert_leading_characters(outstrbuf, INT_PRINT_OUTBUF_SIZE, ' ', pad_n); // insert leading characters
            }
            outstr += pad_n; // advance pointer to the end of the string
        }
    }

    // copy string to output
    int copy_len = string_copy(outbuf, outstrbuf, free_space);
    return copy_len;
}

static int pfn_integer(va_list *va, FmtWord *fmt, char *outbuf, size_t free_space) {
    uint64_t u = 0;
    bool negative = false;
    if (fmt->type == SIGNED_INTEGER) { // for signed integers
        int64_t si;
        if (fmt->length == LEN_NORMAL) { // ...without length specifiers
            si = va_arg((*va), int);
        } else { // ...with length specifiers
            si = va_arg((*va), int64_t);
        }

        // absolute value
        if (si < 0) {
            negative = true;
            u = -si;
        } else {
            u = si;
        }
    } else if (fmt->type == UNSIGNED_INTEGER || fmt->type == UNSIGNED_HEXADECIMAL_INT || fmt->type == UNSIGNED_HEXADECIMAL_INT_UPPERCASE) { // for UNsigned integers
        if (fmt->length == LEN_NORMAL) { // ...without length specifiers
            unsigned int d = va_arg((*va), unsigned int);
            u = d;
        } else { // ...with length specifiers
            u = va_arg((*va), uint64_t);
        }
    }

    // print number
    int copy_len = print_number(u, negative, fmt, outbuf, free_space);
    return copy_len;
}

#define DECIMAL_POINT ('.')

static int pfn_double(va_list *va, FmtWord *fmt, char *outbuf, size_t free_space) {
    // get passed double variable
    double d = va_arg((*va), double);
    bool negative = d < 0;
    if (negative) {
        d *= -1;
    }

    // normalize if exponential form is required
    int exponent = 0;
    if (fmt->type == DOUBLE_EXPONENTIAL) {
        double q = d < 1.0 ? 10.0 : 0.1; // quotient
        int d_exp = d < 1.0 ? -1 : 1; // shift per iteration in exponent
        while (!(d >= 1.0 && d < 10.0)) {
            d *= q;
            exponent += d_exp;
        }
    }

    // formatting of the integer part
    FmtWord int_fmt = {.flags = fmt->flags, .type = UNSIGNED_INTEGER, .width = fmt->width};

    // separate into integer and fractional part
    uint64_t int_part = (uint64_t) d; // integer part
    int copy_len = print_number(int_part, negative, &int_fmt, outbuf, free_space);
    free_space -= copy_len;
    outbuf += copy_len;

    int sum_copy_len = copy_len; // summed copy length

    // fractional part
    if (fmt->precision > 0) {
        // place decimal point
        *outbuf = DECIMAL_POINT;
        outbuf++;
        free_space--;
        sum_copy_len++;

        *outbuf = '\0';

        // prepare format for printing fractional part
        FmtWord frac_fmt = {.flags = FLAG_NO, .width = -1, .type = UNSIGNED_INTEGER};

        // get "leading zeros" in fractional part
        double d_frac = d - (double) int_part;

        // print leading zeros
        int leading_zeros_printed = 0;
        while ((d_frac * 10.0) < 1.0 && leading_zeros_printed < fmt->precision) {
            d_frac *= 10.0;
            *outbuf = '0';
            outbuf++;
            free_space--;
            sum_copy_len++;
            *outbuf = '\0';
            leading_zeros_printed++;
        }

        // extract fractional part as integer
        d_frac *= (double) power(10, fmt->precision - leading_zeros_printed + 1); // get one more digit
        uint64_t frac_part = (uint64_t) d_frac;
        frac_part = round_to_base(frac_part, 10) / 10; // remove last zero digit (result of rounding)

        // print fractional part
        copy_len = print_number(frac_part, false, &frac_fmt, outbuf, free_space);
        free_space -= copy_len;
        outbuf += copy_len;
        sum_copy_len += copy_len;
    }

    // print exponential if format requires
    if (fmt->type == DOUBLE_EXPONENTIAL) {
        // print 'e'
        *outbuf = 'e';
        outbuf++;
        *outbuf = '\0';
        free_space--;
        sum_copy_len++;

        // print value of exponent
        FmtWord exponent_fmt = {.flags = FLAG_PREPEND_PLUS_SIGN | FLAG_LEADING_ZEROS, .width = 2, .type = UNSIGNED_INTEGER};

        unsigned int exponent_abs = exponent > 0 ? exponent : -exponent;

        copy_len = print_number(exponent_abs, exponent < 0, &exponent_fmt, outbuf, free_space);
        free_space -= copy_len;
        outbuf += copy_len;
        sum_copy_len += copy_len;
    }

    return sum_copy_len;
}

// print character
static int pfn_char(va_list *va, FmtWord *fmt, char *outbuf, size_t free_space) {
    int c = va_arg((*va), int);
    unsigned rep = (fmt->width <= 0) ? 1 : fmt->width; // determine repetition count
    rep = MIN(free_space, rep);
    for (unsigned i = 0; i < rep; i++) {
        outbuf[i] = (char)c;
    }
    outbuf[rep] = '\0';
    return rep;
}

// print string
static int pfn_string(va_list *va, FmtWord *fmt, char *outbuf, size_t free_space) {
    char *str = va_arg((*va), char*);
    return string_copy(outbuf, str, free_space);
}

// format swting assignment table
static FmtTypeDesignatorPair sTypeDesAssignment[] = {{'%',  LITERAL_PERCENT,                    pfn_literal_percent},
                                                     {'d',  SIGNED_INTEGER,                     pfn_integer},
                                                     {'i',  SIGNED_INTEGER,                     pfn_integer},
                                                     {'u',  UNSIGNED_INTEGER,                   pfn_integer},
                                                     {'f',  DOUBLE,                             pfn_double},
                                                     {'e',  DOUBLE_EXPONENTIAL,                 pfn_double},
                                                     {'x',  UNSIGNED_HEXADECIMAL_INT,           pfn_integer},
                                                     {'X',  UNSIGNED_HEXADECIMAL_INT_UPPERCASE, pfn_integer},
                                                     {'p',  UNSIGNED_HEXADECIMAL_INT,           pfn_integer},
                                                     {'s',  STRING,                             pfn_string},
                                                     {'c',  CHARACTER,                          pfn_char},
                                                     {'\0', UNKNOWN} // termination
};

// ------------------------------------------------------------

// try to fetch number from the start of the string
// return: number found OR -1 on failure
static char *fetch_number(char *str, int *num) {
    char *start = str;
    char *end = start;
    *num = 0;
    while ('0' <= *end && '9' >= *end) {
        *num *= 10;
        *num += *end - '0';
        end++;
    }

    if (end == start) {
        *num = -1;
    }

    return end;
}

// get number of arguments from the format string
static int get_number_of_arguments_by_format_string(char *format_str) {
    char *iter = format_str;
    int cnt = 0;
    while (*iter != '\0') {
        if (*iter == FORMAT_DELIMITER) {
            if (*(iter + 1) == '%') { // filter out '%%' literals
                iter++;
            } else {
                cnt++;
            }
        }
        iter++;
    }
    return cnt;
}

// seek for format delimiter ('%')
static char *seek_delimiter(char *str) {
    // iterate over characters until either '%' is found or end of string is reached
    while (*(str) != '\0' && *(str) != FORMAT_DELIMITER) {
        str++;
    }

    // return based on what we found
    if (*str == FORMAT_DELIMITER) {
        return str;
    } else {
        return NULL;
    }
}

// get the the formatting word
// str: input string
// begin: pointer to pointer to the begin of the format word
// length: length of the format word (number of bytes to be copied after)
// return: pointer to unprocessed input string
static char *locate_format_word(char *str, char **begin, size_t *length) {
    char *delim_pos = seek_delimiter(str); // seek for format specifier begin
    if (delim_pos == NULL) { // if not found...
        *length = 0; // set to zero if not found
        return NULL; // ...then return
    }

    // here we have pointer to the '%' character of a format "word"

    // a valid format string has a length at least of 1 byte (i. e. something must follow the '%')
    char *word_start = delim_pos + 1;
    *begin = word_start;

    // search the ending of the format word, which can be either a whitespace or a new '%' character (or the '\0')
    char *word_iter = word_start;
    while ((*word_iter > ' ' || word_iter == word_start) && (*word_iter != FORMAT_DELIMITER || word_iter == word_start) && *word_iter != '\0') {
        word_iter++;
    }

    // now, word_iter points to the first character following the previously found delimiter now belonging to the format word
    char *unproc_text = word_iter;

    // calculate the length of the word
    *length = word_iter - word_start;

    return unproc_text;
}

// fetch format word
// str: input text
// word: output format word (if return value != NULL)
// preceding_text: text before format word
// maxlen: maximum STRING LENGTH of the output
// return: pointer to unprocessed text OR NULL on failure
static char *fetch_format_word(char *str, char *word, char **word_begin, size_t maxlen) {
    // locate word
    size_t len;
    char *unproc_text = locate_format_word(str, word_begin, &len);

    // copy
    string_copy(word, *word_begin, MIN(maxlen, len));

    return unproc_text;
}

// fetch type from designator character
static FmtTypeDesignatorPair *get_type_by_designator(char designator) {
    FmtTypeDesignatorPair *iter = sTypeDesAssignment;
    while (iter->designator != '\0' && iter->designator != designator) {
        iter++;
    }
    return iter;
}

#define DEFAULT_PRINT_PRECISION (6)
#define LENGTH_IS_PARAMETER (-2) // -1 is used for something else

static char sFlags[] = " 0+";

// decide whether the passed character is a flag indicator
static bool is_flag(char c) {
    char *iter = sFlags;
    while (*iter != '\0') {
        if (*iter == c) {
            return true;
        }
        iter++;
    }
    return false;
}

// process format word into format structure
// str: input format string to process
// word: output format specifier
// rewind: number of characters to rewind input (some characters may be considered wrongly as being part of the format word)
// return: 0 on success, -1 on failure
static int process_format_word(char *str, FmtWord *word, int *rewind) {
    // 1.: look for flags
    word->flags = FLAG_NO;
    while (is_flag(*str)) {
        switch (*str) {
            case '0':
                word->flags |= FLAG_LEADING_ZEROS;
                break;
            case ' ':
                word->flags |= FLAG_LEADING_SPACES;
                break;
            case '+':
                word->flags |= FLAG_PREPEND_PLUS_SIGN;
                break;
        }
        str++;
    }

    // 2.: look for width
    if (*str == '*') { // parametered width
        str++;
        word->width = LENGTH_IS_PARAMETER; // read length from the varargs
    } else {
        str = fetch_number(str, &(word->width));
    }

    // 3.: look for precision
    word->precision = DEFAULT_PRINT_PRECISION; // default double precision
    if (*str == '.') {
        str++;
        str = fetch_number(str, &(word->precision));
    }

    // 4.: look for length
    word->length = LEN_NORMAL;
    if (*str == 'l') {
        word->length = LEN_LONG;
        str++;
    }

    // 5.: get type from the designator
    word->pTypeDes = get_type_by_designator(*str);
    word->type = word->pTypeDes->type;
    *rewind = string_length(str + 1);

    if (word->type == UNKNOWN) {
        return -1;
    } else {
        return 0;
    }
}

#define MAX_FORMAT_WORD_LEN (15)

unsigned long int vembfmt(char *str, unsigned long int len, char *format, va_list args) {
    // process format string
    long int free_space = len;
    char *unproc_text = format;
    char *unproc_text_next = NULL;
    char word_str[MAX_FORMAT_WORD_LEN + 1];
    char *word_begin;
    size_t sum_copy_len = 0;
    while ((*unproc_text) && (unproc_text_next = fetch_format_word(unproc_text, word_str, &word_begin, MAX_FORMAT_WORD_LEN)) && free_space > 0) {
        // print preceding text
        word_begin--;
        int copy_len = MIN((word_begin - unproc_text), free_space);
        string_copy(str, unproc_text, copy_len);
        free_space -= copy_len;
        str += copy_len;
        sum_copy_len += copy_len;

        // print data
        FmtWord word = { 0 };
        int rewind;
        process_format_word(word_str, &word, &rewind);
        if (word.type != UNKNOWN) {
            if (word.width == LENGTH_IS_PARAMETER) { // if length is passed in parameter...
                word.width = va_arg(args, unsigned); // read length parameter
            }

#ifdef COMPILE_FOR_LINUX
            int copy_len = word.pTypeDes->fn(args, &word, str, free_space); // variable with the same name!
#else
            int copy_len = word.pTypeDes->fn(&args, &word, str, free_space); // variable with the same name!
#endif
            free_space -= copy_len;
            str += copy_len;
            sum_copy_len += copy_len;
        }

        // advance pointer in unprocessed text
        unproc_text = unproc_text_next - rewind;
    }

    // also copy last part of the string not containing any formatting sequences
    if (unproc_text != NULL) {
        sum_copy_len += string_copy(str, unproc_text, free_space);
    }

    return sum_copy_len;
}

unsigned long int embfmt(char *str, unsigned long int len, char *format, ...) {
    // get number of expected arguments and initiate va_list usage
    int argc = get_number_of_arguments_by_format_string(format);

    va_list args;
    va_start(args, format);

    unsigned long int copy_len = vembfmt(str, len, format, args);

    va_end(args);
    return copy_len;
}