User:A22347/Printf
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Here is an example printf implementation. It does not support hexadecimal floating point numbers. It can easily be ported into a kernel or userspace library as it only relies on a small number of standard functions.
#include <stdio.h> //putchar
#include <string.h> //strcpy, strcat, memcpy, memset
#include <ctype.h> //isdigit
#include <stdbool.h>
#include <stdint.h>
#include <stdarg.h>
char* __int_str(intmax_t i, char b[], int base, bool plusSignIfNeeded, bool spaceSignIfNeeded,
int paddingNo, bool justify, bool zeroPad) {
char digit[32] = {0};
memset(digit, 0, 32);
strcpy(digit, "0123456789");
if (base == 16) {
strcat(digit, "ABCDEF");
} else if (base == 17) {
strcat(digit, "abcdef");
base = 16;
}
char* p = b;
if (i < 0) {
*p++ = '-';
i *= -1;
} else if (plusSignIfNeeded) {
*p++ = '+';
} else if (!plusSignIfNeeded && spaceSignIfNeeded) {
*p++ = ' ';
}
intmax_t shifter = i;
do {
++p;
shifter = shifter / base;
} while (shifter);
*p = '\0';
do {
*--p = digit[i % base];
i = i / base;
} while (i);
int padding = paddingNo - (int)strlen(b);
if (padding < 0) padding = 0;
if (justify) {
while (padding--) {
if (zeroPad) {
b[strlen(b)] = '0';
} else {
b[strlen(b)] = ' ';
}
}
} else {
char a[256] = {0};
while (padding--) {
if (zeroPad) {
a[strlen(a)] = '0';
} else {
a[strlen(a)] = ' ';
}
}
strcat(a, b);
strcpy(b, a);
}
return b;
}
void displayCharacter(char c, int* a) {
putchar(c);
*a += 1;
}
void displayString(char* c, int* a) {
for (int i = 0; c[i]; ++i) {
displayCharacter(c[i], a);
}
}
int vprintf (const char* format, va_list list)
{
int chars = 0;
char intStrBuffer[256] = {0};
for (int i = 0; format[i]; ++i) {
char specifier = '\0';
char length = '\0';
int lengthSpec = 0;
int precSpec = 0;
bool leftJustify = false;
bool zeroPad = false;
bool spaceNoSign = false;
bool altForm = false;
bool plusSign = false;
bool emode = false;
int expo = 0;
if (format[i] == '%') {
++i;
bool extBreak = false;
while (1) {
switch (format[i]) {
case '-':
leftJustify = true;
++i;
break;
case '+':
plusSign = true;
++i;
break;
case '#':
altForm = true;
++i;
break;
case ' ':
spaceNoSign = true;
++i;
break;
case '0':
zeroPad = true;
++i;
break;
default:
extBreak = true;
break;
}
if (extBreak) break;
}
while (isdigit(format[i])) {
lengthSpec *= 10;
lengthSpec += format[i] - 48;
++i;
}
if (format[i] == '*') {
lengthSpec = va_arg(list, int);
++i;
}
if (format[i] == '.') {
++i;
while (isdigit(format[i])) {
precSpec *= 10;
precSpec += format[i] - 48;
++i;
}
if (format[i] == '*') {
precSpec = va_arg(list, int);
++i;
}
} else {
precSpec = 6;
}
if (format[i] == 'h' || format[i] == 'l' || format[i] == 'j' ||
format[i] == 'z' || format[i] == 't' || format[i] == 'L') {
length = format[i];
++i;
if (format[i] == 'h') {
length = 'H';
} else if (format[i] == 'l') {
length = 'q';
++i;
}
}
specifier = format[i];
memset(intStrBuffer, 0, 256);
int base = 10;
if (specifier == 'o') {
base = 8;
specifier = 'u';
if (altForm) {
displayString("0", &chars);
}
}
if (specifier == 'p') {
base = 16;
length = 'z';
specifier = 'u';
}
switch (specifier) {
case 'X':
base = 16;
case 'x':
base = base == 10 ? 17 : base;
if (altForm) {
displayString("0x", &chars);
}
case 'u':
{
switch (length) {
case 0:
{
unsigned int integer = va_arg(list, unsigned int);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 'H':
{
unsigned char integer = (unsigned char) va_arg(list, unsigned int);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 'h':
{
unsigned short int integer = va_arg(list, unsigned int);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 'l':
{
unsigned long integer = va_arg(list, unsigned long);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 'q':
{
unsigned long long integer = va_arg(list, unsigned long long);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 'j':
{
uintmax_t integer = va_arg(list, uintmax_t);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 'z':
{
size_t integer = va_arg(list, size_t);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 't':
{
ptrdiff_t integer = va_arg(list, ptrdiff_t);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
default:
break;
}
break;
}
case 'd':
case 'i':
{
switch (length) {
case 0:
{
int integer = va_arg(list, int);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 'H':
{
signed char integer = (signed char) va_arg(list, int);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 'h':
{
short int integer = va_arg(list, int);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 'l':
{
long integer = va_arg(list, long);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 'q':
{
long long integer = va_arg(list, long long);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 'j':
{
intmax_t integer = va_arg(list, intmax_t);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 'z':
{
size_t integer = va_arg(list, size_t);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
case 't':
{
ptrdiff_t integer = va_arg(list, ptrdiff_t);
__int_str(integer, intStrBuffer, base, plusSign, spaceNoSign, lengthSpec, leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
break;
}
default:
break;
}
break;
}
case 'c':
{
if (length == 'l') {
displayCharacter(va_arg(list, wint_t), &chars);
} else {
displayCharacter(va_arg(list, int), &chars);
}
break;
}
case 's':
{
displayString(va_arg(list, char*), &chars);
break;
}
case 'n':
{
switch (length) {
case 'H':
*(va_arg(list, signed char*)) = chars;
break;
case 'h':
*(va_arg(list, short int*)) = chars;
break;
case 0: {
int* a = va_arg(list, int*);
*a = chars;
break;
}
case 'l':
*(va_arg(list, long*)) = chars;
break;
case 'q':
*(va_arg(list, long long*)) = chars;
break;
case 'j':
*(va_arg(list, intmax_t*)) = chars;
break;
case 'z':
*(va_arg(list, size_t*)) = chars;
break;
case 't':
*(va_arg(list, ptrdiff_t*)) = chars;
break;
default:
break;
}
break;
}
case 'e':
case 'E':
emode = true;
case 'f':
case 'F':
case 'g':
case 'G':
{
double floating = va_arg(list, double);
while (emode && floating >= 10) {
floating /= 10;
++expo;
}
int form = lengthSpec - precSpec - expo - (precSpec || altForm ? 1 : 0);
if (emode) {
form -= 4; // 'e+00'
}
if (form < 0) {
form = 0;
}
__int_str(floating, intStrBuffer, base, plusSign, spaceNoSign, form, \
leftJustify, zeroPad);
displayString(intStrBuffer, &chars);
floating -= (int) floating;
for (int i = 0; i < precSpec; ++i) {
floating *= 10;
}
intmax_t decPlaces = (intmax_t) (floating + 0.5);
if (precSpec) {
displayCharacter('.', &chars);
__int_str(decPlaces, intStrBuffer, 10, false, false, 0, false, false);
intStrBuffer[precSpec] = 0;
displayString(intStrBuffer, &chars);
} else if (altForm) {
displayCharacter('.', &chars);
}
break;
}
case 'a':
case 'A':
//ACK! Hexadecimal floating points...
break;
default:
break;
}
if (specifier == 'e') {
displayString("e+", &chars);
} else if (specifier == 'E') {
displayString("E+", &chars);
}
if (specifier == 'e' || specifier == 'E') {
__int_str(expo, intStrBuffer, 10, false, false, 2, false, true);
displayString(intStrBuffer, &chars);
}
} else {
displayCharacter(format[i], &chars);
}
}
return chars;
}
__attribute__ ((format (printf, 1, 2))) int printf (const char* format, ...)
{
va_list list;
va_start (list, format);
int i = vprintf (format, list);
va_end (list);
return i;
}