351 lines
7.8 KiB
Rust
351 lines
7.8 KiB
Rust
/*
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Module: float
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*/
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/**
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* Section: String Conversions
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*/
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/*
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Function: to_str_common
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Converts a float to a string
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Parameters:
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num - The float value
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digits - The number of significant digits
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exact - Whether to enforce the exact number of significant digits
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*/
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fn to_str_common(num: float, digits: uint, exact: bool) -> str {
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let (num, accum) = num < 0.0 ? (-num, "-") : (num, "");
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let trunc = num as uint;
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let frac = num - (trunc as float);
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accum += uint::str(trunc);
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if frac == 0.0 || digits == 0u { ret accum; }
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accum += ".";
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let i = digits;
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let epsilon = 1. / pow_uint_to_uint_as_float(10u, i);
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while i > 0u && (frac >= epsilon || exact) {
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frac *= 10.0;
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epsilon *= 10.0;
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let digit = frac as uint;
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accum += uint::str(digit);
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frac -= digit as float;
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i -= 1u;
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}
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ret accum;
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}
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/*
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Function: to_str
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Converts a float to a string with exactly the number of provided significant
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digits
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Parameters:
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num - The float value
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digits - The number of significant digits
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*/
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fn to_str_exact(num: float, digits: uint) -> str {
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to_str_common(num, digits, true)
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}
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/*
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Function: to_str
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Converts a float to a string with a maximum number of significant digits
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Parameters:
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num - The float value
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digits - The number of significant digits
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*/
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fn to_str(num: float, digits: uint) -> str {
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to_str_common(num, digits, false)
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}
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/*
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Function: from_str
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Convert a string to a float
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This function accepts strings such as
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* "3.14"
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* "+3.14", equivalent to "3.14"
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* "-3.14"
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* "2.5E10", or equivalently, "2.5e10"
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* "2.5E-10"
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* "", or, equivalently, "." (understood as 0)
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* "5."
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* ".5", or, equivalently, "0.5"
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Leading and trailing whitespace are ignored.
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Parameters:
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num - A string, possibly empty.
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Returns:
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<NaN> If the string did not represent a valid number.
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Otherwise, the floating-point number represented [num].
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*/
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fn from_str(num: str) -> float {
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let num = str::trim(num);
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let pos = 0u; //Current byte position in the string.
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//Used to walk the string in O(n).
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let len = str::byte_len(num); //Length of the string, in bytes.
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if len == 0u { ret 0.; }
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let total = 0f; //Accumulated result
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let c = 'z'; //Latest char.
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//The string must start with one of the following characters.
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alt str::char_at(num, 0u) {
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'-' | '+' | '0' to '9' | '.' {}
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_ { ret NaN; }
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}
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//Determine if first char is '-'/'+'. Set [pos] and [neg] accordingly.
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let neg = false; //Sign of the result
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alt str::char_at(num, 0u) {
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'-' {
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neg = true;
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pos = 1u;
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}
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'+' {
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pos = 1u;
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}
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_ {}
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}
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//Examine the following chars until '.', 'e', 'E'
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while(pos < len) {
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let char_range = str::char_range_at(num, pos);
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c = char_range.ch;
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pos = char_range.next;
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alt c {
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'0' to '9' {
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total = total * 10f;
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total += ((c as int) - ('0' as int)) as float;
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}
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'.' | 'e' | 'E' {
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break;
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}
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_ {
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ret NaN;
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}
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}
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}
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if c == '.' {//Examine decimal part
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let decimal = 1.f;
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while(pos < len) {
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let char_range = str::char_range_at(num, pos);
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c = char_range.ch;
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pos = char_range.next;
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alt c {
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'0' | '1' | '2' | '3' | '4' | '5' | '6'| '7' | '8' | '9' {
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decimal /= 10.f;
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total += (((c as int) - ('0' as int)) as float)*decimal;
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}
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'e' | 'E' {
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break;
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}
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_ {
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ret NaN;
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}
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}
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}
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}
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if (c == 'e') | (c == 'E') {//Examine exponent
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let exponent = 0u;
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let neg_exponent = false;
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if(pos < len) {
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let char_range = str::char_range_at(num, pos);
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c = char_range.ch;
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alt c {
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'+' {
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pos = char_range.next;
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}
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'-' {
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pos = char_range.next;
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neg_exponent = true;
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}
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_ {}
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}
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while(pos < len) {
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let char_range = str::char_range_at(num, pos);
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c = char_range.ch;
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alt c {
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'0' | '1' | '2' | '3' | '4' | '5' | '6'| '7' | '8' | '9' {
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exponent *= 10u;
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exponent += ((c as uint) - ('0' as uint));
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}
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_ {
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break;
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}
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}
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pos = char_range.next;
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}
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let multiplier = pow_uint_to_uint_as_float(10u, exponent);
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//Note: not [int::pow], otherwise, we'll quickly
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//end up with a nice overflow
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if neg_exponent {
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total = total / multiplier;
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} else {
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total = total * multiplier;
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}
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} else {
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ret NaN;
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}
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}
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if(pos < len) {
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ret NaN;
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} else {
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if(neg) {
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total *= -1f;
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}
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ret total;
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}
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}
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/**
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* Section: Arithmetics
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*/
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/*
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Function: pow_uint_to_uint_as_float
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Compute the exponentiation of an integer by another integer as a float.
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Parameters:
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x - The base.
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pow - The exponent.
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Returns:
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<NaN> of both `x` and `pow` are `0u`, otherwise `x^pow`.
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*/
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fn pow_uint_to_uint_as_float(x: uint, pow: uint) -> float {
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if x == 0u {
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if pow == 0u {
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ret NaN;
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}
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ret 0.;
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}
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let my_pow = pow;
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let total = 1f;
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let multiplier = x as float;
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while (my_pow > 0u) {
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if my_pow % 2u == 1u {
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total = total * multiplier;
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}
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my_pow /= 2u;
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multiplier *= multiplier;
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}
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ret total;
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}
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/**
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* Section: Constants
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*/
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//TODO: Once this is possible, replace the body of these functions
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//by an actual constant.
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/* Const: NaN */
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const NaN: float = 0./0.;
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/* Predicate: isNaN */
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pure fn isNaN(f: float) -> bool { f != f }
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/* Const: infinity */
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const infinity: float = 1./0.;
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/* Const: neg_infinity */
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const neg_infinity: float = -1./0.;
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/* Function: add */
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pure fn add(x: float, y: float) -> float { ret x + y; }
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/* Function: sub */
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pure fn sub(x: float, y: float) -> float { ret x - y; }
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/* Function: mul */
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pure fn mul(x: float, y: float) -> float { ret x * y; }
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/* Function: div */
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pure fn div(x: float, y: float) -> float { ret x / y; }
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/* Function: rem */
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pure fn rem(x: float, y: float) -> float { ret x % y; }
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/* Predicate: lt */
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pure fn lt(x: float, y: float) -> bool { ret x < y; }
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/* Predicate: le */
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pure fn le(x: float, y: float) -> bool { ret x <= y; }
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/* Predicate: eq */
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pure fn eq(x: float, y: float) -> bool { ret x == y; }
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/* Predicate: ne */
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pure fn ne(x: float, y: float) -> bool { ret x != y; }
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/* Predicate: ge */
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pure fn ge(x: float, y: float) -> bool { ret x >= y; }
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/* Predicate: gt */
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pure fn gt(x: float, y: float) -> bool { ret x > y; }
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/*
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Predicate: positive
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Returns true if `x` is a positive number, including +0.0 and +Infinity.
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*/
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pure fn positive(x: float) -> bool { ret x > 0. || (1./x) == infinity; }
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/*
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Predicate: negative
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Returns true if `x` is a negative number, including -0.0 and -Infinity.
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*/
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pure fn negative(x: float) -> bool { ret x < 0. || (1./x) == neg_infinity; }
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/*
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Predicate: nonpositive
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Returns true if `x` is a negative number, including -0.0 and -Infinity.
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(This is the same as `float::negative`.)
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*/
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pure fn nonpositive(x: float) -> bool {
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ret x < 0. || (1./x) == neg_infinity;
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}
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/*
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Predicate: nonnegative
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Returns true if `x` is a positive number, including +0.0 and +Infinity.
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(This is the same as `float::positive`.)
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*/
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pure fn nonnegative(x: float) -> bool {
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ret x > 0. || (1./x) == infinity;
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}
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//
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// Local Variables:
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// mode: rust
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// fill-column: 78;
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// indent-tabs-mode: nil
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// c-basic-offset: 4
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// buffer-file-coding-system: utf-8-unix
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// End:
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//
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