From 51630f179562687f27d1e5eb9f3c370de4f01622 Mon Sep 17 00:00:00 2001
From: Mike <45243121+tankf33der@users.noreply.github.com>
Date: Sun, 17 Aug 2025 19:25:15 +0300
Subject: [PATCH] math.big: fix bytes() if bit_len is divisible by 60, add
 tests (#25126)

---
 vlib/math/big/big_test.v | 11 +++++++++++
 vlib/math/big/integer.v  |  6 +++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/vlib/math/big/big_test.v b/vlib/math/big/big_test.v
index 15c422b0a..59905c573 100644
--- a/vlib/math/big/big_test.v
+++ b/vlib/math/big/big_test.v
@@ -991,3 +991,14 @@ fn test_pow2_is_power_of_2() {
 		assert big.two_int.pow(n).is_power_of_2(), 'pow2: ${n}'
 	}
 }
+
+fn test_bytes_from_bytes() {
+	input := ['0', '9999999999999999999999999999999999999', '783086277830859384',
+		'890810171456467012368983335296321559']
+	for n in input {
+		a := big.integer_from_string(n)!
+		b, _ := a.bytes()
+		c := big.integer_from_bytes(b)
+		assert a.str() == c.str()
+	}
+}
diff --git a/vlib/math/big/integer.v b/vlib/math/big/integer.v
index 8f169301e..78be0d261 100644
--- a/vlib/math/big/integer.v
+++ b/vlib/math/big/integer.v
@@ -891,7 +891,11 @@ pub fn (a Integer) bytes() ([]u8, int) {
 		bits_in_byte = 0
 	}
 	// MSB digit
-	for i := bit_len % digit_bits - 1; i >= 0; i-- {
+	mut msb_bits := bit_len % digit_bits
+	if msb_bits == 0 {
+		msb_bits = digit_bits
+	}
+	for i := msb_bits - 1; i >= 0; i-- {
 		bit = u8((digit >> i) & 1)
 		current_byte = (current_byte << 1) | u8(bit)
 		bits_in_byte++
-- 
2.39.5