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Fix significant figure rounding #390

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Fix significant figure rounding #390

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70 changes: 51 additions & 19 deletions core/src/num/biguint.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,10 +2,10 @@ use crate::error::{FendError, Interrupt};
use crate::format::Format;
use crate::interrupt::test_int;
use crate::num::bigrat::sign::Sign;
use crate::num::{Base, Exact, Range, RangeBound, out_of_range};
use crate::num::{out_of_range, Base, Exact, Range, RangeBound};
use crate::result::FResult;
use crate::serialize::CborValue;
use std::cmp::{Ordering, max};
use std::cmp::{max, Ordering};
use std::{fmt, hash};

#[derive(Clone)]
Expand Down Expand Up @@ -1379,16 +1379,11 @@ impl Format for BigUint {
type Out = FormattedBigUint;

fn format<I: Interrupt>(&self, params: &Self::Params, int: &I) -> FResult<Exact<Self::Out>> {
let base_prefix = if params.write_base_prefix {
Some(params.base)
} else {
None
};

if self.is_zero() {
return Ok(Exact::new(
FormattedBigUint {
base: base_prefix,
base: params.base,
write_base_prefix: params.write_base_prefix,
ty: FormattedBigUintType::Zero,
},
true,
Expand All @@ -1400,7 +1395,8 @@ impl Format for BigUint {
if num.value_len() == 1 && params.base.base_as_u8() == 10 && params.sf_limit.is_none() {
Exact::new(
FormattedBigUint {
base: base_prefix,
base: params.base,
write_base_prefix: params.write_base_prefix,
ty: FormattedBigUintType::Simple(num.get(0)),
},
true,
Expand Down Expand Up @@ -1454,7 +1450,8 @@ impl Format for BigUint {
.is_none_or(|sf| sf >= output.len() - num_leading_zeroes);
Exact::new(
FormattedBigUint {
base: base_prefix,
base: params.base,
write_base_prefix: params.write_base_prefix,
ty: FormattedBigUintType::Complex(output, params.sf_limit),
},
exact,
Expand All @@ -1474,25 +1471,60 @@ enum FormattedBigUintType {
#[must_use]
#[derive(Debug)]
pub(crate) struct FormattedBigUint {
base: Option<Base>,
base: Base,
write_base_prefix: bool,
ty: FormattedBigUintType,
}

impl fmt::Display for FormattedBigUint {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
if let Some(base) = self.base {
base.write_prefix(f)?;
if self.write_base_prefix {
self.base.write_prefix(f)?;
}
match &self.ty {
FormattedBigUintType::Zero => write!(f, "0")?,
FormattedBigUintType::Simple(i) => write!(f, "{i}")?,
FormattedBigUintType::Complex(s, sf_limit) => {
for (i, ch) in s.chars().rev().enumerate() {
if sf_limit.is_some() && &Some(i) >= sf_limit {
write!(f, "0")?;
} else {
write!(f, "{ch}")?;
let base_as_u32: u32 = u32::from(self.base.base_as_u8());
let mut rev_chars: Vec<char> = s.chars().rev().collect();

if let Some(sf) = sf_limit
&& *sf > 0 && *sf < rev_chars.len() {
let num_truncated = rev_chars.len() - sf;
let dropped_char = rev_chars[*sf];
let val = dropped_char.to_digit(base_as_u32).unwrap_or(0);

// Keep only the significant figures we want
rev_chars.truncate(*sf);

// Check if we should round up (equivalent to fraction >= 1/2)
if val * 2 >= base_as_u32 {
let mut carry = 1u32;
for i in (0..*sf).rev() {
let d = rev_chars[i].to_digit(base_as_u32).unwrap_or(0) + carry;
if d >= base_as_u32 {
rev_chars[i] = '0';
carry = 1;
} else {
rev_chars[i] = char::from_digit(d, base_as_u32).unwrap();
carry = 0;
break;
}
}
if carry > 0 {
rev_chars.insert(0, '1');
}
}

// Pad with trailing zeros to maintain the original length
let target_len = rev_chars.len() + num_truncated;
while rev_chars.len() < target_len {
rev_chars.push('0');
}
}

for ch in rev_chars {
write!(f, "{ch}")?;
}
}
}
Expand Down
50 changes: 34 additions & 16 deletions core/tests/integration_tests.rs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
use fend_core::{Context, evaluate};
use fend_core::{evaluate, Context};

#[track_caller]
fn test_serialization_roundtrip(context: &mut Context) {
Expand Down Expand Up @@ -125,12 +125,10 @@ fn two_pi() {
#[test]
fn pi_to_fraction() {
let mut ctx = Context::new();
assert!(
evaluate("pi to fraction", &mut ctx)
.unwrap()
.get_main_result()
.starts_with("approx.")
);
assert!(evaluate("pi to fraction", &mut ctx)
.unwrap()
.get_main_result()
.starts_with("approx."));
}

const DIVISION_BY_ZERO_ERROR: &str = "division by zero";
Expand Down Expand Up @@ -4240,17 +4238,17 @@ fn sf_3() {

#[test]
fn sf_4() {
test_eval("1234567.55645 to 4 sf", "approx. 1234000");
test_eval("1234567.55645 to 4 sf", "approx. 1235000");
}

#[test]
fn sf_5() {
test_eval("1234567.55645 to 5 sf", "approx. 1234500");
test_eval("1234567.55645 to 5 sf", "approx. 1234600");
}

#[test]
fn sf_6() {
test_eval("1234567.55645 to 6 sf", "approx. 1234560");
test_eval("1234567.55645 to 6 sf", "approx. 1234570");
}

#[test]
Expand Down Expand Up @@ -4298,6 +4296,26 @@ fn sf_small_2() {
test_eval("pi / 1000000 to 2 sf", "approx. 0.0000031");
}

#[test]
fn sf_hex_17f_1() {
test_eval("0x17f to 1 sf", "approx. 0x100");
}

#[test]
fn sf_hex_17f_2() {
test_eval("0x17f to 2 sf", "approx. 0x180");
}

#[test]
fn sf_hex_ff_1() {
test_eval("0xff to 1 sf", "approx. 0x100");
}

#[test]
fn sf_hex_ff_2() {
test_eval("0xff to 2 sf", "0xff");
}

#[test]
fn sf_rounding_integer_carry() {
test_eval("123.9 to 3 sf", "approx. 124");
Expand Down Expand Up @@ -4380,12 +4398,12 @@ fn million_pi_3_sf() {

#[test]
fn million_pi_4_sf() {
test_eval("1e6 pi to 4 sf", "approx. 3141000");
test_eval("1e6 pi to 4 sf", "approx. 3142000");
}

#[test]
fn million_pi_5_sf() {
test_eval("1e6 pi to 5 sf", "approx. 3141500");
test_eval("1e6 pi to 5 sf", "approx. 3141600");
}

#[test]
Expand Down Expand Up @@ -4430,17 +4448,17 @@ fn large_integer_to_3_sf() {

#[test]
fn large_integer_to_4_sf() {
test_eval("1234567 to 4 sf", "approx. 1234000");
test_eval("1234567 to 4 sf", "approx. 1235000");
}

#[test]
fn large_integer_to_5_sf() {
test_eval("1234567 to 5 sf", "approx. 1234500");
test_eval("1234567 to 5 sf", "approx. 1234600");
}

#[test]
fn large_integer_to_6_sf() {
test_eval("1234567 to 6 sf", "approx. 1234560");
test_eval("1234567 to 6 sf", "approx. 1234570");
}

#[test]
Expand All @@ -4465,7 +4483,7 @@ fn large_integer_to_10_sf() {

#[test]
fn trailing_zeroes_sf_1() {
test_eval("1234560 to 5sf", "approx. 1234500");
test_eval("1234560 to 5sf", "approx. 1234600");
}

#[test]
Expand Down
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