When manually creating a raw bitcoin tx, how does one determine whether the r or s values require more zeros?

Question

Supposedly, if an R or S value will equal a "negative" number, one must append zeros to it and alter the "length" descriptor for the value to reflect that. When manually creating a raw tx how does one determine whether one's R and or S values require the addition of these extra byte(s)? All conversions I do with a hex calculator always show positive numbers.

Answer 1

If the first byte is greater than or equal to 0x80 (128), then you need to add a leading zero byte. You can do 0x80 & first_byte. If the result is zero, no padding is needed.

Answer 2

There are unsigned and signed numbers. R + S values are obviously interpreted as signed numbers, and when the first bit of the number is high, then you have a number, which is interpreted as negative. So all signatures' S and R values beginning with "more than 7F"

Pieter explained it here: extract:

• R and S are signed integers, encoded as a big-endian byte sequence. They are stored in as few bytes as possible (i.e., no 0x00 padding in front), except that a single 0x00 byte is needed and even required when the byte following it has its highest bit set, to prevent it from being interpreted as a negative number.