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/*
Module: float
*/
/**
* Section: String Conversions
*/
/*
Function: to_str
Converts a float to a string
Parameters:
num - The float value
digits: The number of significant digits
*/
fn to_str(num: float, digits: uint) -> str {
let accum = if num < 0.0 { num = -num; "-" } else { "" };
let trunc = num as uint;
let frac = num - (trunc as float);
accum += uint::str(trunc);
if frac == 0.0 || digits == 0u { ret accum; }
accum += ".";
while digits > 0u && frac > 0.0 {
frac *= 10.0;
let digit = frac as uint;
accum += uint::str(digit);
frac -= digit as float;
digits -= 1u;
}
ret accum;
}
/*
Function: from_str
Convert a string to a float
This function accepts strings such as
* "3.14"
* "+3.14", equivalent to "3.14"
* "-3.14"
* "2.5E10", or equivalently, "2.5e10"
* "2.5E-10"
* "", or, equivalently, "." (understood as 0)
* "5."
* ".5", or, equivalently, "0.5"
Parameters:
num - A string, possibly empty.
Returns:
<NaN> If the string did not represent a valid number.
Otherwise, the floating-point number represented [num].
*/
fn from_str(num: str) -> float {
let pos = 0u; //Current byte position in the string.
//Used to walk the string in O(n).
let len = str::byte_len(num); //Length of the string, in bytes.
if len == 0u { ret 0.; }
let total = 0f; //Accumulated result
let c = 'z'; //Latest char.
//Determine if first char is '-'/'+'. Set [pos] and [neg] accordingly.
let neg = false; //Sign of the result
alt str::char_at(num, 0u) {
'-' {
neg = true;
pos = 1u;
}
'+' {
pos = 1u;
}
_ {}
}
//Examine the following chars until '.', 'e', 'E'
while(pos < len) {
let char_range = str::char_range_at(num, pos);
c = char_range.ch;
pos = char_range.next;
alt c {
'0' to '9' {
total = total * 10f;
total += ((c as int) - ('0' as int)) as float;
}
_ {
break;
}
}
}
if c == '.' {//Examine decimal part
let decimal = 1.f;
while(pos < len) {
let char_range = str::char_range_at(num, pos);
c = char_range.ch;
pos = char_range.next;
alt c {
'0' | '1' | '2' | '3' | '4' | '5' | '6'| '7' | '8' | '9' {
decimal /= 10.f;
total += (((c as int) - ('0' as int)) as float)*decimal;
}
_ {
break;
}
}
}
}
if (c == 'e') | (c == 'E') {//Examine exponent
let exponent = 0u;
let neg_exponent = false;
if(pos < len) {
let char_range = str::char_range_at(num, pos);
c = char_range.ch;
alt c {
'+' {
pos = char_range.next;
}
'-' {
pos = char_range.next;
neg_exponent = true;
}
_ {}
}
while(pos < len) {
let char_range = str::char_range_at(num, pos);
c = char_range.ch;
pos = char_range.next;
alt c {
'0' | '1' | '2' | '3' | '4' | '5' | '6'| '7' | '8' | '9' {
exponent *= 10u;
exponent += ((c as uint) - ('0' as uint));
}
_ {
break;
}
}
}
let multiplier = pow_uint_to_uint_as_float(10u, exponent);
//Note: not [int::pow], otherwise, we'll quickly
//end up with a nice overflow
if neg_exponent {
total = total / multiplier;
} else {
total = total * multiplier;
}
}
}
if(pos < len) {
ret NaN();
} else {
if(neg) {
total *= -1f;
}
ret total;
}
}
/**
* Section: Arithmetics
*/
/*
Function: pow_uint_to_uint_as_float
Compute the exponentiation of an integer by another integer as a float.
Parameters:
x - The base.
pow - The exponent.
Returns:
<NaN> of both `x` and `pow` are `0u`, otherwise `x^pow`.
*/
fn pow_uint_to_uint_as_float(x: uint, pow: uint) -> float {
if x == 0u {
if pow == 0u {
ret NaN();
}
ret 0.;
}
let my_pow = pow;
let total = 1f;
let multiplier = x as float;
while (my_pow > 0u) {
if my_pow % 2u == 1u {
total = total * multiplier;
}
my_pow /= 2u;
multiplier *= multiplier;
}
ret total;
}
/**
* Section: Constants
*/
//TODO: Once this is possible, replace the body of these functions
//by an actual constant.
/* Function: NaN */
fn NaN() -> float {
ret 0./0.;
}
/* Function: infinity */
fn infinity() -> float {
ret 1./0.;
}
/* Function: neg_infinity */
fn neg_infinity() -> float {
ret -1./0.;
}
//
// Local Variables:
// mode: rust
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// compile-command: "make -k -C $RBUILD 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
// End:
//
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