Implement exp2() and log2(), and make ir_unop_exp and ir_unop_log be base e.

Making the base e functions IR operations is not a clear win.  i965
doesn't support it, it doesn't look like r600 supports it, but r500
does. It should be easily supportable as a lowering pass, though.
diff --git a/builtin_function.cpp b/builtin_function.cpp
index 7cd08d7..ef6af20 100644
--- a/builtin_function.cpp
+++ b/builtin_function.cpp
@@ -77,6 +77,22 @@
 }
 
 static void
+generate_exp2(exec_list *instructions,
+	      ir_variable **declarations,
+	      const glsl_type *type)
+{
+   generate_unop(instructions, declarations, type, ir_unop_exp2);
+}
+
+static void
+generate_log2(exec_list *instructions,
+	      ir_variable **declarations,
+	      const glsl_type *type)
+{
+   generate_unop(instructions, declarations, type, ir_unop_log2);
+}
+
+static void
 generate_rsq(exec_list *instructions,
 	       ir_variable **declarations,
 	       const glsl_type *type)
@@ -278,8 +294,8 @@
    make_gentype_function(symtab, instructions, "pow", 2, generate_pow);
    make_gentype_function(symtab, instructions, "exp", 1, generate_exp);
    make_gentype_function(symtab, instructions, "log", 1, generate_log);
-   /* FINISHME: exp2() */
-   /* FINISHME: log2() */
+   make_gentype_function(symtab, instructions, "exp2", 1, generate_exp2);
+   make_gentype_function(symtab, instructions, "log2", 1, generate_log2);
    make_gentype_function(symtab, instructions, "sqrt", 1, generate_sqrt);
    make_gentype_function(symtab, instructions, "inversesqrt", 1, generate_rsq);
    make_gentype_function(symtab, instructions, "abs", 1, generate_abs);
diff --git a/ir.h b/ir.h
index 4590528..600a2cd 100644
--- a/ir.h
+++ b/ir.h
@@ -228,6 +228,8 @@
    ir_unop_sqrt,
    ir_unop_exp,
    ir_unop_log,
+   ir_unop_exp2,
+   ir_unop_log2,
    ir_unop_f2i,      /**< Float-to-integer conversion. */
    ir_unop_i2f,      /**< Integer-to-float conversion. */
    ir_unop_u2f,      /**< Unsigned-to-float conversion. */
diff --git a/ir_print_visitor.cpp b/ir_print_visitor.cpp
index 8b2080f..aeff280 100644
--- a/ir_print_visitor.cpp
+++ b/ir_print_visitor.cpp
@@ -96,6 +96,8 @@
       "sqrt",
       "exp",
       "log",
+      "exp2",
+      "log2",
       "f2i",
       "i2f",
       "u2f",