diff --git a/benchmarks/ctype_benchmark.cpp b/benchmarks/ctype_benchmark.cpp
index eab0133..c6c23b0 100644
--- a/benchmarks/ctype_benchmark.cpp
+++ b/benchmarks/ctype_benchmark.cpp
@@ -19,65 +19,78 @@
 #include <benchmark/benchmark.h>
 #include "util.h"
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalnum_y1, isalnum('A'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalnum_y2, isalnum('a'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalnum_y3, isalnum('0'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalnum_n, isalnum('_'));
+// Avoid optimization.
+volatile int A = 'A';
+volatile int a = 'a';
+volatile int X = 'X';
+volatile int x = 'x';
+volatile int backspace = '\b';
+volatile int del = '\x7f';
+volatile int space = ' ';
+volatile int tab = '\t';
+volatile int zero = '0';
+volatile int underscore = '_';
+volatile int top_bit_set = 0x88;
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalpha_y1, isalpha('A'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalpha_y2, isalpha('a'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalpha_n, isalpha('_'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalnum_y1, isalnum(A));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalnum_y2, isalnum(a));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalnum_y3, isalnum(zero));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalnum_n, isalnum(underscore));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isascii_y, isascii('x'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isascii_n, isascii(0x88));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalpha_y1, isalpha(A));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalpha_y2, isalpha(a));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isalpha_n, isalpha(underscore));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isblank_y1, isblank(' '));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isblank_y2, isblank('\t'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isblank_n, isblank('_'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isascii_y, isascii(x));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isascii_n, isascii(top_bit_set));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_iscntrl_y1, iscntrl('\b'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_iscntrl_y2, iscntrl('\x7f'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_iscntrl_n, iscntrl('_'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isblank_y1, isblank(space));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isblank_y2, isblank(tab));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isblank_n, isblank(underscore));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isdigit_y, iscntrl('0'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isdigit_n, iscntrl('_'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_iscntrl_y1, iscntrl(backspace));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_iscntrl_y2, iscntrl(del));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_iscntrl_n, iscntrl(underscore));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isgraph_y1, isgraph('A'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isgraph_y2, isgraph('a'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isgraph_y3, isgraph('0'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isgraph_y4, isgraph('_'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isgraph_n, isgraph(' '));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isdigit_y, iscntrl(zero));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isdigit_n, iscntrl(underscore));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_islower_y, islower('x'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_islower_n, islower('X'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isgraph_y1, isgraph(A));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isgraph_y2, isgraph(a));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isgraph_y3, isgraph(zero));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isgraph_y4, isgraph(underscore));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isgraph_n, isgraph(space));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isprint_y1, isprint('A'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isprint_y2, isprint('a'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isprint_y3, isprint('0'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isprint_y4, isprint('_'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isprint_y5, isprint(' '));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isprint_n, isprint('\b'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_islower_y, islower(x));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_islower_n, islower(X));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_ispunct_y, ispunct('_'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_ispunct_n, ispunct('A'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isprint_y1, isprint(A));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isprint_y2, isprint(a));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isprint_y3, isprint(zero));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isprint_y4, isprint(underscore));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isprint_y5, isprint(space));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isprint_n, isprint(backspace));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isspace_y1, isspace(' '));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isspace_y2, isspace('\t'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isspace_n, isspace('A'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_ispunct_y, ispunct(underscore));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_ispunct_n, ispunct(A));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isupper_y, isupper('X'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isupper_n, isupper('x'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isspace_y1, isspace(space));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isspace_y2, isspace(tab));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isspace_n, isspace(A));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isxdigit_y1, isxdigit('0'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isxdigit_y2, isxdigit('a'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isxdigit_y3, isxdigit('A'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isxdigit_n, isxdigit('_'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isupper_y, isupper(X));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isupper_n, isupper(x));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_toascii_y, isascii('x'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_toascii_n, isascii(0x88));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isxdigit_y1, isxdigit(zero));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isxdigit_y2, isxdigit(a));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isxdigit_y3, isxdigit(A));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_isxdigit_n, isxdigit(underscore));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_tolower_y, tolower('X'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_tolower_n, tolower('x'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_toascii_y, isascii(x));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_toascii_n, isascii(top_bit_set));
 
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_toupper_y, toupper('x'));
-BIONIC_TRIVIAL_BENCHMARK(BM_ctype_toupper_n, toupper('X'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_tolower_y, tolower(X));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_tolower_n, tolower(x));
+
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_toupper_y, toupper(x));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_toupper_n, toupper(X));