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Diffstat (limited to 'libc/misc/internals/dtostr.c')
| -rw-r--r-- | libc/misc/internals/dtostr.c | 271 |
1 files changed, 271 insertions, 0 deletions
diff --git a/libc/misc/internals/dtostr.c b/libc/misc/internals/dtostr.c new file mode 100644 index 000000000..d9ab80bbb --- /dev/null +++ b/libc/misc/internals/dtostr.c @@ -0,0 +1,271 @@ +/* + * Copyright (C) 2000 Manuel Novoa III + * + * Function: const char *__dtostr(double x) + * + * This was written for uClibc to give it the ability to at least output + * floating point values in exponential form. No formatting is done. + * No trailing 0's are removed. Number of digits generated is not + * runtime selectable. It does however handle +/- infinity and nan on i386. + * + * The goal was usable floating point %e-type output in minimal size. For + * me, "gcc -c -Os -fomit-frame-pointer dtostr.c && size dtostr.o" gives + * text data bss dec hex filename + * 535 9 26 570 23a dtostr.o (WANT_EXP_FORM = 1) + * 530 9 26 565 235 dtostr.o (WANT_EXP_FORM = 0) + * + * Output is of the form [-][#].######{e|E}{+|-}##. Choices of upper or + * lower case exponent character, and initial digit/initial decimal forms + * are compile-time options. Number of digits generated is also selected + * at compile time (MAX_DIGITS). + * + * Notes: + * + * The primary objective of this implementation was minimal size while + * maintaining reasonable accuracy. It should also be fairly portable, + * as not assumptions are made about the bit-layout of doubles. + * + * It should be too difficult to convert this to handle long doubles on i386. + * For information, see the comments below. + * + * There are 2 compile-time options below, as well as some tuning parameters. + * + * TODO: + * long double and/or float version? (note: for float can trim code some). + */ + +/*****************************************************************************/ +/* OPTIONS */ +/*****************************************************************************/ + +/* + * Set this if you want output results with 1 digit before the decimal point. + * If this is 0, all digits follow a leading decimal point. + */ +#define WANT_EXP_FORM 1 + +/* + * Set if you want exponent character 'E' rather than 'e'. + */ +#define EXP_UPPERCASE 1 + +/*****************************************************************************/ +/* Don't change anything that follows unless you know what you're doing. */ +/*****************************************************************************/ + +/* + * Configuration for the scaling power table. Ignoring denormals, you + * should have 2**EXP_TABLE_SIZE >= MAX_DBL_EXP >= 2**(EXP_TABLE_SIZE-1). + * The minimum for standard C is 6. For IEEE 8bit doubles, 9 suffices. + */ +#define EXP_TABLE_SIZE 9 + +/* + * Set this to the maximum number of digits you want converted. + * Conversion is done in blocks of DIGITS_PER_BLOCK (9 by default) digits. + * 17 digits suffices to uniquely determine a double on i386. + */ +#define MAX_DIGITS 17 + +/* + * This is really only used to check for infinities. The macro produces + * smaller code for i386 and, since this is tested before any floating point + * calculations, it doesn't appear to suffer from the excess precision problem + * caused by the FPU that strtod had. If it causes problems, call the function + * and compile zoicheck.c with -ffloat-store. + */ +#if 1 +#define _zero_or_inf_check(x) ( x == (x/4) ) +#else +extern int _zero_or_inf_check(double x); +#endif + +/* + * Fairly portable nan check. Bitwise for i386 generated larger code. + * If you have a better version, comment this out. + */ +#define isnan(x) (x != x) + +/*****************************************************************************/ +/* Don't change anything that follows peroid!!! ;-) */ +/*****************************************************************************/ + +#include <float.h> +#include <limits.h> + +/* + * Set things up for the scaling power table. + */ + +#if EXP_TABLE_SIZE < 6 +#error EXP_TABLE_SIZE should be at least 6 to comply with standards +#endif + +#define EXP_TABLE_MAX (1U<<(EXP_TABLE_SIZE-1)) + +/* + * Only bother checking if this is too small. + * Throw in some play for denormals ( roughly O(-324) vs O(-307) on i386 ). + */ + +#if (3+DBL_DIG-DBL_MIN_10_EXP)/2 > EXP_TABLE_MAX +#error larger EXP_TABLE_SIZE needed +#endif + +/* + * With 32 bit ints, we can get 9 digits per block. + */ +#define DIGITS_PER_BLOCK 9 + +#if (INT_MAX >> 30) +#define DIGIT_BLOCK_TYPE int +#elif (LONG_MAX >> 30) +#define DIGIT_BLOCK_TYPE long +#else +#error need at least 32 bit longs +#endif + +/* + * This is kind of a place-holder for LONG_DOUBLE support to show what I + * think needs to be changed. I haven't tried it though. Changing this + * from 3 to 4 and converting double to long double should work on i386. + * DON'T FORGET to increase EXP_TABLE_SIZE and MAX_DIGITS. + * DON'T FORGET the "larger EXP_TABLE_SIZE needed" check above. + */ +#define MAX_EXP_DIGITS 3 + +/*****************************************************************************/ + +#define NUM_DIGIT_BLOCKS ((MAX_DIGITS+DIGITS_PER_BLOCK-1)/DIGITS_PER_BLOCK) + +static char infstr[] = " inf"; /* save space for a - sign */ +static char nanstr[] = "nan"; + +/* extra space for '-', '.', 'e+###', and nul */ +/*static char buf[ 5 + MAX_EXP_DIGITS + NUM_DIGIT_BLOCKS * DIGITS_PER_BLOCK];*/ +#define BUF_SIZE ( 5 + MAX_EXP_DIGITS + NUM_DIGIT_BLOCKS * DIGITS_PER_BLOCK ) +/*****************************************************************************/ + +const char *__dtostr(char *buf, double x) +{ + double exp_table[EXP_TABLE_SIZE]; + double p10; + DIGIT_BLOCK_TYPE digit_block; /* int of at least 32 bits */ + int i, j; + int exp, exp_neg; + int negative = 0; + char *pos; + + if (isnan(x)) { /* nan check */ + return nanstr; + } + + if (x == 0) { /* handle 0 now to avoid false positive */ + exp = 0; /* with inf test, and to avoid scaling */ + goto GENERATE_DIGITS; /* note: time vs space tradeoff */ + } + + if (x < 0) { /* convert negatives to positives */ + negative = 1; + x = -x; + } + + if (_zero_or_inf_check(x)) { /* must be inf since zero handled above */ + pos = infstr + 1; + goto DO_SIGN; + } + + /* need to build the scaling table */ + for (i = 0, p10 = 10 ; i < EXP_TABLE_SIZE ; i++) { + exp_table[i] = p10; + p10 *= p10; + } + + exp_neg = 0; + if (x < 1e8) { /* do we need to scale up or down? */ + exp_neg = 1; + } + +#if WANT_EXP_FORM + exp = DIGITS_PER_BLOCK - 1; +#else + exp = DIGITS_PER_BLOCK; +#endif + + i = EXP_TABLE_SIZE; + j = EXP_TABLE_MAX; + while ( i-- ) { /* scale x such that 1e8 <= x < 1e9 */ + if (exp_neg) { + if (x * exp_table[i] < 1e9) { + x *= exp_table[i]; + exp -= j; + } + } else { + if (x / exp_table[i] >= 1e8) { + x /= exp_table[i]; + exp += j; + } + } + j >>= 1; + } + + GENERATE_DIGITS: + pos = buf - BUF_SIZE + 1 + DIGITS_PER_BLOCK + 1; /* leave space for '.' and - */ + + for (i = 0 ; i < NUM_DIGIT_BLOCKS ; ++i ) { + digit_block = (int) x; + x = (x - digit_block) * 1e9; + for (j = 0 ; j < DIGITS_PER_BLOCK ; j++) { + *--pos = '0' + (digit_block % 10); + digit_block /= 10; + } + pos += (2*DIGITS_PER_BLOCK); + } + pos -= (DIGITS_PER_BLOCK*(NUM_DIGIT_BLOCKS+1))-MAX_DIGITS; + + /* start generating the exponent */ +#if EXP_UPPERCASE + *pos = 'E'; +#else + *pos = 'e'; +#endif + *++pos = '+'; + if (exp < 0) { + *pos = '-'; + exp = -exp; + } + pos += 3; /* WARNING: Assumes max exp < 1000!!! */ + if (exp >= 100) { + ++pos; +#if MAX_EXP_DIGITS > 4 +#error need to modify exponent string generation code +#elif MAX_EXP_DIGITS > 3 + if (exp >= 1000) { /* WARNING: hasn't been checked */ + ++pos; /* but should work */ + } +#endif + } + *pos = '\0'; + + for (j = 0 ; (j < 2) || exp ; j++) { /* standard says at least 2 digits */ + *--pos = '0' + (exp % 10); + exp /= 10; + } + + /* insert the decimal point */ + pos = buf - BUF_SIZE + 1; + +#if WANT_EXP_FORM + *pos = *(pos+1); + *(pos+1) = '.'; +#else + *pos = '.'; +#endif + + DO_SIGN: + if (negative) { + *--pos = '-'; + } + + return pos; +} |