Fix formatRate, support negative exponents in parseFixed

.changeset/tricky-goats-mix.md

@@ -0,0 +1,5 @@
+---
+"@delvtech/fixed-point-wasm": patch
+---
+
+Added support for negative exponents to `parseFixed`, e.g., `parseFixed(1e-18)`.

apps/hyperdrive-trading/src/base/formatRate.ts

@@ -13,6 +13,7 @@ export function formatRate({
   let formatted = fixed(rate).format({
     percent: true,
     decimals: 2,
+    trailingZeros: true,
   });
 
   if (formatted === "-0.00%") {

apps/hyperdrive-trading/src/testing/setupTests.ts

@@ -1,3 +1,8 @@
+import * as fixedPoint from "@delvtech/fixed-point-wasm";
 import { beforeEach } from "vitest";
 
-beforeEach(() => {});
+beforeEach(() => {
+  // This is safe to call multiple times. Internally it will return early if
+  // the WASM module has already been initialized.
+  fixedPoint.initSync(fixedPoint.wasmBuffer);
+});

crates/fixed-point-wasm/src/utils.rs

@@ -71,28 +71,27 @@ pub fn fixed(value: Numberish, decimals: Option<u8>) -> Result<WasmFixedPoint, E
 pub fn parse_fixed(value: Numberish, decimals: Option<u8>) -> Result<WasmFixedPoint, Error> {
     // If the value is already a fixed-point number, it's already scaled.
     if value.is_fixed_point() == Some(true) {
-        return fixed(value, decimals);
+        return WasmFixedPoint::new(value, decimals);
     }
 
     let decimals = decimals.unwrap_or(INNER_DECIMALS);
     let mut s = value.to_string().as_string().unwrap_or_default();
 
     if s.contains("e") {
-        s = value.as_string().unwrap_or_default();
         let mut parts = s.split("e");
         let mantissa_str = parts.next().unwrap_or_default();
         let exponent_str = parts.next().unwrap_or_default();
-        let exponent = u8::from_str_radix(exponent_str, 10).to_result()?;
+        let exponent = i8::from_str_radix(exponent_str, 10).to_result()?;
         let mut mantissa_parts = mantissa_str.split(".");
         let int_str = mantissa_parts.next().unwrap_or_default();
         let fraction_str = mantissa_parts.next().unwrap_or_default();
         let mut inner = I256::from_dec_str(&format!("{int_str}{fraction_str}"))
             .to_result()?
             .fixed();
-        let fraction_digits = fraction_str.len() as u8;
+        let fraction_digits = fraction_str.len() as i8;
 
         if fraction_digits > exponent {
-            inner /= (10u32.pow((fraction_digits - exponent) as u32)).into();
+            inner /= (10u128.pow((fraction_digits - exponent) as u32)).into();
             return Ok(WasmFixedPoint { inner, decimals });
         }