cutils: add functions for IEC and SI prefixes

Extract the knowledge of IEC and SI prefixes out of size_to_str and
freq_to_str, so that it can be reused when printing statistics.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qemu/cutils.h

@@ -1,6 +1,24 @@
 #ifndef QEMU_CUTILS_H
 #define QEMU_CUTILS_H
 
+/*
+ * si_prefix:
+ * @exp10: exponent of 10, a multiple of 3 between -18 and 18 inclusive.
+ *
+ * Return a SI prefix (n, u, m, K, M, etc.) corresponding
+ * to the given exponent of 10.
+ */
+const char *si_prefix(unsigned int exp10);
+
+/*
+ * iec_binary_prefix:
+ * @exp2: exponent of 2, a multiple of 10 between 0 and 60 inclusive.
+ *
+ * Return an IEC binary prefix (Ki, Mi, etc.) corresponding
+ * to the given exponent of 2.
+ */
+const char *iec_binary_prefix(unsigned int exp2);
+
 /**
  * pstrcpy:
  * @buf: buffer to copy string into

tests/unit/test-cutils.c

@@ -2450,6 +2450,50 @@ static void test_qemu_strtosz_metric(void)
     g_assert(endptr == str + 7);
 }
 
+static void test_freq_to_str(void)
+{
+    g_assert_cmpstr(freq_to_str(999), ==, "999 Hz");
+    g_assert_cmpstr(freq_to_str(1000), ==, "1 KHz");
+    g_assert_cmpstr(freq_to_str(1010), ==, "1.01 KHz");
+}
+
+static void test_size_to_str(void)
+{
+    g_assert_cmpstr(size_to_str(0), ==, "0 B");
+    g_assert_cmpstr(size_to_str(1), ==, "1 B");
+    g_assert_cmpstr(size_to_str(1016), ==, "0.992 KiB");
+    g_assert_cmpstr(size_to_str(1024), ==, "1 KiB");
+    g_assert_cmpstr(size_to_str(512ull << 20), ==, "512 MiB");
+}
+
+static void test_iec_binary_prefix(void)
+{
+    g_assert_cmpstr(iec_binary_prefix(0), ==, "");
+    g_assert_cmpstr(iec_binary_prefix(10), ==, "Ki");
+    g_assert_cmpstr(iec_binary_prefix(20), ==, "Mi");
+    g_assert_cmpstr(iec_binary_prefix(30), ==, "Gi");
+    g_assert_cmpstr(iec_binary_prefix(40), ==, "Ti");
+    g_assert_cmpstr(iec_binary_prefix(50), ==, "Pi");
+    g_assert_cmpstr(iec_binary_prefix(60), ==, "Ei");
+}
+
+static void test_si_prefix(void)
+{
+    g_assert_cmpstr(si_prefix(-18), ==, "a");
+    g_assert_cmpstr(si_prefix(-15), ==, "f");
+    g_assert_cmpstr(si_prefix(-12), ==, "p");
+    g_assert_cmpstr(si_prefix(-9), ==, "n");
+    g_assert_cmpstr(si_prefix(-6), ==, "u");
+    g_assert_cmpstr(si_prefix(-3), ==, "m");
+    g_assert_cmpstr(si_prefix(0), ==, "");
+    g_assert_cmpstr(si_prefix(3), ==, "K");
+    g_assert_cmpstr(si_prefix(6), ==, "M");
+    g_assert_cmpstr(si_prefix(9), ==, "G");
+    g_assert_cmpstr(si_prefix(12), ==, "T");
+    g_assert_cmpstr(si_prefix(15), ==, "P");
+    g_assert_cmpstr(si_prefix(18), ==, "E");
+}
+
 int main(int argc, char **argv)
 {
     g_test_init(&argc, &argv, NULL);
@@ -2729,5 +2773,13 @@ int main(int argc, char **argv)
     g_test_add_func("/cutils/strtosz/metric",
                     test_qemu_strtosz_metric);
 
+    g_test_add_func("/cutils/size_to_str",
+                    test_size_to_str);
+    g_test_add_func("/cutils/freq_to_str",
+                    test_freq_to_str);
+    g_test_add_func("/cutils/iec_binary_prefix",
+                    test_iec_binary_prefix);
+    g_test_add_func("/cutils/si_prefix",
+                    test_si_prefix);
     return g_test_run();
 }

util/cutils.c

@@ -872,6 +872,25 @@ int parse_debug_env(const char *name, int max, int initial)
     return debug;
 }
 
+const char *si_prefix(unsigned int exp10)
+{
+    static const char *prefixes[] = {
+        "a", "f", "p", "n", "u", "m", "", "K", "M", "G", "T", "P", "E"
+    };
+
+    exp10 += 18;
+    assert(exp10 % 3 == 0 && exp10 / 3 < ARRAY_SIZE(prefixes));
+    return prefixes[exp10 / 3];
+}
+
+const char *iec_binary_prefix(unsigned int exp2)
+{
+    static const char *prefixes[] = { "", "Ki", "Mi", "Gi", "Ti", "Pi", "Ei" };
+
+    assert(exp2 % 10 == 0 && exp2 / 10 < ARRAY_SIZE(prefixes));
+    return prefixes[exp2 / 10];
+}
+
 /*
  * Return human readable string for size @val.
  * @val can be anything that uint64_t allows (no more than "16 EiB").
@@ -880,7 +899,6 @@ int parse_debug_env(const char *name, int max, int initial)
  */
 char *size_to_str(uint64_t val)
 {
-    static const char *suffixes[] = { "", "Ki", "Mi", "Gi", "Ti", "Pi", "Ei" };
     uint64_t div;
     int i;
 
@@ -891,25 +909,23 @@ char *size_to_str(uint64_t val)
      * (see e41b509d68afb1f for more info)
      */
     frexp(val / (1000.0 / 1024.0), &i);
-    i = (i - 1) / 10;
+    i = (i - 1) / 10 * 10;
-    div = 1ULL << (i * 10);
+    div = 1ULL << i;
 
-    return g_strdup_printf("%0.3g %sB", (double)val / div, suffixes[i]);
+    return g_strdup_printf("%0.3g %sB", (double)val / div, iec_binary_prefix(i));
 }
 
 char *freq_to_str(uint64_t freq_hz)
 {
-    static const char *const suffixes[] = { "", "K", "M", "G", "T", "P", "E" };
     double freq = freq_hz;
-    size_t idx = 0;
+    size_t exp10 = 0;
 
     while (freq >= 1000.0) {
         freq /= 1000.0;
-        idx++;
+        exp10 += 3;
     }
-    assert(idx < ARRAY_SIZE(suffixes));
 
-    return g_strdup_printf("%0.3g %sHz", freq, suffixes[idx]);
+    return g_strdup_printf("%0.3g %sHz", freq, si_prefix(exp10));
 }
 
 int qemu_pstrcmp0(const char **str1, const char **str2)