fn ensure_positive(a: &mut Vec<u8>) {
    if a[0] >= 0x80 {
        a.insert(0, 0x00);
    }
}
// Prepend the big-endian integer with leading zeros if needed, in order to
// make it a positive integer. For example, when the input is 0xffff,
// it will be parsed as a negative number, hence we need to change it to
// 0x00ffff.
Prepend the big-endian integer with leading zeros if needed, in order to
make it a positive integer. For example, when the input is 0xffff,
it will be parsed as a negative number, hence we need to change it to
0x00ffff.
Prepend the big - endian integer with leading zeros if needed in order to make it a positive integer . For example when the input is 0xffff it will be parsed as a negative number hence we need to change it to 0x00ffff .
fn ensure_positive(a: &mut Vec<u8>) {
    if a[0] >= 0x80 {
        a.insert(0, 0x00);
    }
}
fn ensure_positive ( a : & mut Vec < u8 > ) { if a [ 0 ] >= 0x80 { a . insert ( 0 , 0x00 ) ; } }
Prepend the big-endian integer with leading zeros if needed, in order to
make it a positive integer.
Prepend the big - endian integer with leading zeros if needed in order to make it a positive integer .
a
&mut Vec<u8>
a
&mut Vec<u8>