Length of a Sumac sequence A Sumac sequence starts with two integers: t1 and t2.

The next term, t3, = t1 - t2

More generally, tn = tn-2 - tn-1

The sequence ends when tn &lt; 0.

Your challenge: Write a program or function that prints the length of a Sumac sequence, starting with t1 and t2.


t1 and t2 are integers within your language's range.
Standard loopholes apply.


Test cases

t1  t2       sumac_len(t1,t2)

120  71      5
101  42      3
500  499     4
387  1       3


Bonus street cred:

3    -128    1
-314 73      2


This is code-golf, so shortest answer in bytes wins.
Husk, 8 bytes

→V&lt;¡oG-↔


Takes input as a 2-element list.
Try it online!

Explanation

→V&lt;¡oG-↔  Implicit input, say p=[101,42]
   ¡      Iterate on p:
       ↔    Reverse: [42,101]
    oG-     Cumulative reduce by subtraction: [42,59]
          Result is infinite list [[101,42],[42,59],[59,-17],[-17,76],[76,-93]...
 V&lt;       Find the first index where adjacent pairs are lexicographically increasing.
          In our example [42,59] &lt; [59,-17], so this gives 2.
→         Increment: 3