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; }
