Add math:log2/1

10 files changed, 37 insertions, 4 deletions

diff --git a/erts/configure.in b/erts/configure.in
index 1676d3d216..6bea197a80 100644
--- a/erts/configure.in
+++ b/erts/configure.in
@@ -4905,6 +4905,11 @@ LDFLAGS="$LDFLAGS $sanitizers"
 ])
 
 dnl ----------------------------------------------------------------------
+dnl Check for log2
+dnl ----------------------------------------------------------------------
+AC_CHECK_FUNCS([log2])
+
+dnl ----------------------------------------------------------------------
 dnl Output the result.
 dnl ----------------------------------------------------------------------
 
diff --git a/erts/emulator/beam/bif.tab b/erts/emulator/beam/bif.tab
index aea3224342..1d0d214e77 100644
--- a/erts/emulator/beam/bif.tab
+++ b/erts/emulator/beam/bif.tab
@@ -194,6 +194,7 @@ bif math:erf/1
 bif math:erfc/1
 bif math:exp/1
 bif math:log/1
+bif math:log2/1
 bif math:log10/1
 bif math:sqrt/1
 bif math:atan2/2
diff --git a/erts/emulator/beam/erl_math.c b/erts/emulator/beam/erl_math.c
index 16d4fdc09c..9b864628db 100644
--- a/erts/emulator/beam/erl_math.c
+++ b/erts/emulator/beam/erl_math.c
@@ -207,6 +207,24 @@ BIF_RETTYPE math_log_1(BIF_ALIST_1)
     return math_call_1(BIF_P, log, BIF_ARG_1);
 }
 
+#ifdef HAVE_LOG2
+static double
+log2_wrapper(double x)
+{
+    return log2(x);
+}
+#else
+static double
+log2_wrapper(double x)
+{
+    return log(x) / 0.6931471805599453; /* log(2.0); */
+}
+#endif
+
+BIF_RETTYPE math_log2_1(BIF_ALIST_1)
+{
+    return math_call_1(BIF_P, log2_wrapper, BIF_ARG_1);
+}
 
 BIF_RETTYPE math_log10_1(BIF_ALIST_1)
 {
diff --git a/lib/asn1/src/asn1ct_imm.erl b/lib/asn1/src/asn1ct_imm.erl
index bdd14871d1..1e112d6ad3 100644
--- a/lib/asn1/src/asn1ct_imm.erl
+++ b/lib/asn1/src/asn1ct_imm.erl
@@ -1580,7 +1580,7 @@ do_combine_put_bits(_, _, _) ->
     throw(impossible).
 
 debit(Budget0, Alternatives) ->
-    case Budget0 - log2(Alternatives) of
+    case Budget0 - math:log2(Alternatives) of
 	Budget when Budget > 0.0 ->
 	    Budget;
 	_ ->
@@ -1593,8 +1593,6 @@ num_clauses([_|T], N) ->
     num_clauses(T, N+1);
 num_clauses([], N) -> N.
 
-log2(N) ->
-    math:log(N) / math:log(2.0).
 
 collect_put_bits(Imm) ->
     lists:splitwith(fun({put_bits,V,_,_}) when is_integer(V) -> true;
diff --git a/lib/compiler/src/beam_type.erl b/lib/compiler/src/beam_type.erl
index cdddad4153..d9713cef0d 100644
--- a/lib/compiler/src/beam_type.erl
+++ b/lib/compiler/src/beam_type.erl
@@ -469,6 +469,7 @@ is_math_bif(erf, 1) -> true;
 is_math_bif(erfc, 1) -> true;
 is_math_bif(exp, 1) -> true;
 is_math_bif(log, 1) -> true;
+is_math_bif(log2, 1) -> true;
 is_math_bif(log10, 1) -> true;
 is_math_bif(sqrt, 1) -> true;
 is_math_bif(atan2, 2) -> true;
diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl
index 0acc7a227f..c156cf79fe 100644
--- a/lib/compiler/src/beam_validator.erl
+++ b/lib/compiler/src/beam_validator.erl
@@ -1818,6 +1818,7 @@ return_type_math(erf, 1) -> {float,[]};
 return_type_math(erfc, 1) -> {float,[]};
 return_type_math(exp, 1) -> {float,[]};
 return_type_math(log, 1) -> {float,[]};
+return_type_math(log2, 1) -> {float,[]};
 return_type_math(log10, 1) -> {float,[]};
 return_type_math(sqrt, 1) -> {float,[]};
 return_type_math(atan2, 2) -> {float,[]};
diff --git a/lib/compiler/src/erl_bifs.erl b/lib/compiler/src/erl_bifs.erl
index 6c75538194..bcc2297250 100644
--- a/lib/compiler/src/erl_bifs.erl
+++ b/lib/compiler/src/erl_bifs.erl
@@ -134,6 +134,7 @@ is_pure(math, erf, 1) -> true;
 is_pure(math, erfc, 1) -> true;
 is_pure(math, exp, 1) -> true;
 is_pure(math, log, 1) -> true;
+is_pure(math, log2, 1) -> true;
 is_pure(math, log10, 1) -> true;
 is_pure(math, pow, 2) -> true;
 is_pure(math, sin, 1) -> true;
diff --git a/lib/compiler/test/float_SUITE.erl b/lib/compiler/test/float_SUITE.erl
index afc04fd440..fb8da37f4f 100644
--- a/lib/compiler/test/float_SUITE.erl
+++ b/lib/compiler/test/float_SUITE.erl
@@ -118,6 +118,7 @@ math_functions(Config) when is_list(Config) ->
     ?line 0.0 = math:sinh(0),
     ?line 1.0 = math:cosh(0),
     ?line 0.0 = math:tanh(0),
+    1.0 = math:log2(2),
     ?line 1.0 = math:log10(10),
     ?line -1.0 = math:cos(math:pi()),
     ?line 1.0 = math:exp(0),
@@ -136,6 +137,7 @@ math_functions(Config) when is_list(Config) ->
     ?line 0.0 = math:sinh(id(0)),
     ?line 1.0 = math:cosh(id(0)),
     ?line 0.0 = math:tanh(id(0)),
+    1.0 = math:log2(id(2)),
     ?line 1.0 = math:log10(id(10)),
     ?line 1.0 = math:exp(id(0)),
     ?line 0.0 = math:log(id(1)),
diff --git a/lib/stdlib/doc/src/math.xml b/lib/stdlib/doc/src/math.xml
index 43cd20e726..7cfc8a1175 100644
--- a/lib/stdlib/doc/src/math.xml
+++ b/lib/stdlib/doc/src/math.xml
@@ -67,6 +67,7 @@
       <name name="atanh" arity="1"/>
       <name name="exp" arity="1"/>
       <name name="log" arity="1"/>
+      <name name="log2" arity="1"/>
       <name name="log10" arity="1"/>
       <name name="pow" arity="2"/>
       <name name="sqrt" arity="1"/>
diff --git a/lib/stdlib/src/math.erl b/lib/stdlib/src/math.erl
index 98a70b1644..43f736e54c 100644
--- a/lib/stdlib/src/math.erl
+++ b/lib/stdlib/src/math.erl
@@ -24,7 +24,7 @@
 
 -export([sin/1, cos/1, tan/1, asin/1, acos/1, atan/1, atan2/2, sinh/1,
          cosh/1, tanh/1, asinh/1, acosh/1, atanh/1, exp/1, log/1,
-         log10/1, pow/2, sqrt/1, erf/1, erfc/1]).
+         log2/1, log10/1, pow/2, sqrt/1, erf/1, erfc/1]).
 
 -spec acos(X) -> float() when
       X :: number().
@@ -92,6 +92,11 @@ exp(_) ->
 log(_) ->
     erlang:nif_error(undef).
 
+-spec log2(X) -> float() when
+      X :: number().
+log2(_) ->
+    erlang:nif_error(undef).
+
 -spec log10(X) -> float() when
       X :: number().
 log10(_) ->