fix: applied PR review changes

Author: motorina0

README.md

@@ -212,6 +212,18 @@ Returns `null` if result is equal to `0`.
 - `Expected Private` if `!isPrivate(d)`
 - `Expected Tweak` if `tweak` is not in `[0...order - 1]`
 
+### privateNegate (d)
+
+```haskell
+privateNegate :: Buffer -> Buffer
+```
+
+Returns the negation of d on the order n (`n - d`)
+
+##### Throws:
+
+- `Expected Private` if `!isPrivate(d)`
+
 ### xOnlyPointAddTweak (p, tweak)
 
 ```haskell

src/lib.rs

@@ -421,14 +421,12 @@ pub extern "C" fn private_sub() -> i32 {
 #[allow(clippy::missing_panics_doc)]
 #[no_mangle]
 #[export_name = "privateNegate"]
-pub extern "C" fn private_key_negate() -> i32 {
+pub extern "C" fn private_negate() {
     unsafe {
-        if secp256k1_ec_seckey_negate(secp256k1_context_no_precomp, PRIVATE_INPUT.as_mut_ptr()) == 1
-        {
+        assert_eq!(
+            secp256k1_ec_seckey_negate(secp256k1_context_no_precomp, PRIVATE_INPUT.as_mut_ptr()),
             1
-        } else {
-            0
-        }
+        );
     }
 }
 

src_ts/index.ts

@@ -244,14 +244,13 @@ export function privateSub(
   }
 }
 
-export function privateNegate(d: Uint8Array): Uint8Array | null {
+export function privateNegate(d: Uint8Array): Uint8Array {
   validate.validatePrivate(d);
 
   try {
     PRIVATE_KEY_INPUT.set(d);
-    return wasm.privateNegate() === 1
-      ? PRIVATE_KEY_INPUT.slice(0, validate.PRIVATE_KEY_SIZE)
-      : null;
+    wasm.privateNegate();
+    return PRIVATE_KEY_INPUT.slice(0, validate.PRIVATE_KEY_SIZE);
   } finally {
     PRIVATE_KEY_INPUT.fill(0);
   }

src_ts/wasm_loader.ts

@@ -48,7 +48,7 @@ interface Secp256k1WASM {
   pointMultiply: (p: number, outputlen: number) => number;
   privateAdd: () => number;
   privateSub: () => number;
-  privateNegate: () => number;
+  privateNegate: () => void;
   sign: (e: number) => void;
   signRecoverable: (e: number) => 0 | 1 | 2 | 3;
   signSchnorr: (e: number) => void;