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Move from float to Decimal for financial calculations #187

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4d12f05
Fix PLN amount rounding for compliance with tax rules
mbronk Mar 10, 2026
1096aa5
Add opt-in per-transaction rounding (default off per Art. 63 OP)
mbronk Apr 4, 2026
f74f7bd
fixup! Fix PLN amount rounding for compliance with tax rules
mbronk Apr 4, 2026
6b0ce47
Move from float to Decimal for financial calculations
mbronk Apr 4, 2026
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289 changes: 279 additions & 10 deletions Cargo.lock
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2 changes: 2 additions & 0 deletions Cargo.toml
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Expand Up @@ -11,6 +11,7 @@ readme = "README.md"
keywords = ["etrade", "revolut"]
repository = "https://github.com/jczaja/e-trade-tax-return-pl-helper"
homepage = "https://github.com/jczaja/e-trade-tax-return-pl-helper"
default-run = "etradeTaxReturnHelper"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

exclude = [
Expand Down Expand Up @@ -49,5 +50,6 @@ polars = "0.35.4"
csv = "1.3.0"
serde_json = { version = "=1.0.133", optional = true }
holidays = { version = "0.1.0", default-features = false, features = ["PL"] }
rust_decimal = { version = "1.36.0", features = ["macros", "serde-with-float"] }


1 change: 1 addition & 0 deletions REUSE.toml
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Expand Up @@ -10,6 +10,7 @@ SPDX-License-Identifier = "LicenseRef-ETrade-MorganStanley"
path=[
"Cargo.lock",
"assets/etradetaxreturnhelper-640x480.gif",
"rust_decimal.natvis",
]
SPDX-FileCopyrightText = "2025 RustInFinance"
SPDX-License-Identifier = "BSD-3-Clause"
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48 changes: 48 additions & 0 deletions rust_decimal.natvis
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@@ -0,0 +1,48 @@
<?xml version="1.0" encoding="utf-8"?>
<!--
Natvis debugger visualizer for rust_decimal::Decimal.
Lets Visual Studio (and VS Code with C++ debugger) display Decimal values
as human-readable numbers instead of raw {flags, hi, mid, lo} fields.
Referenced via #![debugger_visualizer(natvis_file = "...")] in lib.rs / main.rs.
-->
<AutoVisualizer xmlns="http://schemas.microsoft.com/vstudio/debugger/natvis/2010">
<Type Name="rust_decimal::decimal::Decimal">
<!-- mantissa = hi*2^64 + mid*2^32 + lo; value = (-1)^sign * mantissa / 10^scale -->
<!-- Use (double) casting to show the value. Precision limited to ~15 digits but readable. -->

<!-- Positive values (sign bit = 0) -->
<DisplayString Condition="(flags &gt;&gt; 31) == 0 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 0 &amp;&amp; hi == 0">{(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo),g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 0 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 1 &amp;&amp; hi == 0">{(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 10.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 0 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 2 &amp;&amp; hi == 0">{(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 100.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 0 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 3 &amp;&amp; hi == 0">{(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 1000.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 0 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 4 &amp;&amp; hi == 0">{(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 10000.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 0 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 5 &amp;&amp; hi == 0">{(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 100000.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 0 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 6 &amp;&amp; hi == 0">{(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 1000000.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 0 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 7 &amp;&amp; hi == 0">{(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 10000000.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 0 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 8 &amp;&amp; hi == 0">{(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 100000000.0,g}</DisplayString>

<!-- Negative values (sign bit = 1) -->
<DisplayString Condition="(flags &gt;&gt; 31) == 1 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 0 &amp;&amp; hi == 0">{-(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo),g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 1 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 1 &amp;&amp; hi == 0">{-(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 10.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 1 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 2 &amp;&amp; hi == 0">{-(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 100.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 1 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 3 &amp;&amp; hi == 0">{-(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 1000.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 1 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 4 &amp;&amp; hi == 0">{-(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 10000.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 1 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 5 &amp;&amp; hi == 0">{-(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 100000.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 1 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 6 &amp;&amp; hi == 0">{-(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 1000000.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 1 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 7 &amp;&amp; hi == 0">{-(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 10000000.0,g}</DisplayString>
<DisplayString Condition="(flags &gt;&gt; 31) == 1 &amp;&amp; ((flags &gt;&gt; 16) &amp; 0xFF) == 8 &amp;&amp; hi == 0">{-(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / 100000000.0,g}</DisplayString>

<!-- Fallback for hi != 0 or scale > 8 (large values using full 96-bit mantissa) -->
<DisplayString Condition="(flags &gt;&gt; 31) == 0">~{(double)((double)hi * 18446744073709551616.0 + (double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo)),g} (approx, scale={(flags &gt;&gt; 16) &amp; 0xFF})</DisplayString>
<DisplayString>~{-(double)((double)hi * 18446744073709551616.0 + (double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo)),g} (approx, scale={(flags &gt;&gt; 16) &amp; 0xFF})</DisplayString>

<Expand>
<Item Name="[value]" Condition="hi == 0 &amp;&amp; (flags &gt;&gt; 31) == 0">(double)((unsigned __int64)mid * 4294967296 + (unsigned __int64)lo) / (((flags &gt;&gt; 16) &amp; 0xFF) == 0 ? 1.0 : ((flags &gt;&gt; 16) &amp; 0xFF) == 1 ? 10.0 : ((flags &gt;&gt; 16) &amp; 0xFF) == 2 ? 100.0 : ((flags &gt;&gt; 16) &amp; 0xFF) == 3 ? 1000.0 : ((flags &gt;&gt; 16) &amp; 0xFF) == 4 ? 10000.0 : ((flags &gt;&gt; 16) &amp; 0xFF) == 5 ? 100000.0 : ((flags &gt;&gt; 16) &amp; 0xFF) == 6 ? 1000000.0 : ((flags &gt;&gt; 16) &amp; 0xFF) == 7 ? 10000000.0 : 100000000.0)</Item>
<Item Name="[lo]">lo</Item>
<Item Name="[mid]">mid</Item>
<Item Name="[hi]">hi</Item>
<Item Name="[scale]">(flags &gt;&gt; 16) &amp; 0xFF</Item>
<Item Name="[sign]">(flags &gt;&gt; 31) &amp; 1</Item>
</Expand>
</Type>
</AutoVisualizer>
9 changes: 5 additions & 4 deletions src/bin/gen_exchange_rates.rs
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Expand Up @@ -87,28 +87,29 @@ fn main() {
let mut output_content = String::new();
output_content.push_str("use std::collections::HashMap;\n\n");
output_content.push_str("use etradeTaxReturnHelper::Exchange;\n\n");
output_content.push_str("use rust_decimal::Decimal;\nuse rust_decimal::dec;\n\n");
output_content.push_str("#[allow(clippy::approx_constant)]\n");

output_content.push_str("pub fn get_exchange_rates() -> HashMap<Exchange, f64> {\n");
output_content.push_str("pub fn get_exchange_rates() -> HashMap<Exchange, Decimal> {\n");
output_content.push_str(" let mut exchange_rates = HashMap::new();\n");

for (exchange, kurs) in &kursy_map {
match exchange {
Exchange::USD(data) => {
output_content.push_str(&format!(
" exchange_rates.insert(Exchange::USD(\"{}\".to_string()), {}f64);\n",
" exchange_rates.insert(Exchange::USD(\"{}\".to_string()), dec!({}));\n",
data, kurs
));
}
Exchange::EUR(data) => {
output_content.push_str(&format!(
" exchange_rates.insert(Exchange::EUR(\"{}\".to_string()), {}f64);\n",
" exchange_rates.insert(Exchange::EUR(\"{}\".to_string()), dec!({}));\n",
data, kurs
));
}
Exchange::PLN(data) => {
output_content.push_str(&format!(
" exchange_rates.insert(Exchange::PLN(\"{}\".to_string()), {}f64);\n",
" exchange_rates.insert(Exchange::PLN(\"{}\".to_string()), dec!({}));\n",
data, kurs
));
}
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