From d32376ab227ffebddd8ce8682459fbc979e12749 Mon Sep 17 00:00:00 2001
From: WindOctober <Windocotber@gmail.com>
Date: Sun, 19 Oct 2025 09:15:17 +0000
Subject: [PATCH] Fix: issue #30.

---
 bitcoin-testscripts/src/bitvm/bigint/add.rs  |  3 +++
 bitcoin-testscripts/src/bitvm/bigint/bits.rs | 16 ++++++++++------
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/bitcoin-testscripts/src/bitvm/bigint/add.rs b/bitcoin-testscripts/src/bitvm/bigint/add.rs
index 574642b..1b6874d 100644
--- a/bitcoin-testscripts/src/bitvm/bigint/add.rs
+++ b/bitcoin-testscripts/src/bitvm/bigint/add.rs
@@ -176,6 +176,9 @@ impl<const N_BITS: u32, const LIMB_SIZE: u32> BigIntImpl<N_BITS, LIMB_SIZE> {
     /// This function prevents overflow of the underlying integer types during
     /// left shift operation.
     pub fn lshift_prevent_overflow(bits: u32) -> Script {
+        if bits == 0 {
+            script! {}
+        }
         script! {
             // stack: {limb}
             { 1 << LIMB_SIZE } // {limb} {base}
diff --git a/bitcoin-testscripts/src/bitvm/bigint/bits.rs b/bitcoin-testscripts/src/bitvm/bigint/bits.rs
index 478a972..e90380e 100644
--- a/bitcoin-testscripts/src/bitvm/bigint/bits.rs
+++ b/bitcoin-testscripts/src/bitvm/bigint/bits.rs
@@ -180,13 +180,15 @@ pub fn limb_to_le_bits(num_bits: u32) -> Script {
     }
 }
 
-pub fn limb_to_le_bits_toaltstack(num_bits: u32) -> Script {
+pub fn limb_to_le_bits_toaltstack(num_bits: usize) -> Script {
     if num_bits >= 2 {
         script! {
             { limb_to_le_bits_common(num_bits) }
-            for _ in 0..num_bits {
-                OP_TOALTSTACK
-            }
+            for _ in 0..num_bits { OP_TOALTSTACK }
+        }
+    } else if num_bits == 1 {
+        script! {
+            OP_TOALTSTACK
         }
     } else {
         script! {}
@@ -206,17 +208,19 @@ pub fn limb_to_be_bits(num_bits: u32) -> Script {
     }
 }
 
-pub fn limb_to_be_bits_toaltstack(num_bits: u32) -> Script {
+pub fn limb_to_be_bits_toaltstack(num_bits: usize) -> Script {
     if num_bits >= 2 {
         script! {
             { limb_to_be_bits_common(num_bits) }
             OP_TOALTSTACK
             OP_TOALTSTACK
         }
-    } else {
+    } else if num_bits == 1 {
         script! {
             OP_TOALTSTACK
         }
+    } else {
+        script! {}
     }
 }