From: notoria <notoria@users.noreply.github.com>
Date: Fri, 24 Apr 2020 20:47:24 +0000 (+0200)
Subject: Implemented lsb/2 and msb/2
X-Git-Tag: v0.8.123~110^2
X-Git-Url: https://git.sagredo.dev/?a=commitdiff_plain;h=1873b655a81b118f2604f5d9f7e39eb6d7e6ea52;p=scryer-prolog.git

Implemented lsb/2 and msb/2
---

diff --git a/src/prolog/lib/arithmetic.pl b/src/prolog/lib/arithmetic.pl
new file mode 100644
index 00000000..ab691a09
--- /dev/null
+++ b/src/prolog/lib/arithmetic.pl
@@ -0,0 +1,25 @@
+:- module(arithmetic, [msb/2, lsb/2]).
+
+lsb(X, N) :-
+    builtins:must_be_number(X, lsb/2),
+    (   \+ integer(X) -> throw(error(type_error(integer, X), lsb/2))
+    ;   X < 1 -> throw(error(domain_error(not_less_than_one, X), lsb/2))
+    ;   builtins:can_be_number(N, lsb/2),
+        X1 is X /\ (-X),
+        msb_(X1, -1, N)
+    ).
+
+msb(X, N) :-
+    builtins:must_be_number(X, msb/2),
+    (   \+ integer(X) -> throw(error(type_error(integer, X), msb/2))
+    ;   X < 1 -> throw(error(domain_error(not_less_than_one, X), msb/2))
+    ;   builtins:can_be_number(N, msb/2),
+        X1 is X >> 1,
+        msb_(X1, 0, N)
+    ).
+
+msb_(0, N, N) :- !.
+msb_(X, M, N) :-
+    X1 is X >> 1,
+    M1 is M + 1,
+    msb_(X1, M1, N).