Rejigger how we format the display of bytes.

(Note that this does *not* touch the mega/mebi issue, despite my
recent discussion of it.)

What had been bugging me was that when downloading a file, you'd
see it count up 10.7, 10.8, 10.9, *11*, 11.1.  That is, previously
when we rounded to displaying a trailing zero, we'd clip it off,
which would make a download display like "11.1 / 50.2MB" jiggle to
the left every time the trailing digit lined up.

Now we try to always display three digits, which means we count up
like 98.8, 98.9, *99.0*, 99.1, ... 99.9, 100, ... 101.

This code is after fiddling the test into the shape I wanted it
to be, then making the code produce that behavior.

TEST=covered by unit test, updated with new expected behavior

Review URL: http://codereview.chromium.org/1558025

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@44671 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 24 insertions, 18 deletions

diff --git a/base/string_util.cc b/base/string_util.cc
index 494d09d..fafc106 100644
--- a/base/string_util.cc
+++ b/base/string_util.cc
@@ -887,19 +887,13 @@ std::wstring FormatBytesInternal(int64 bytes,
   for (int i = 0; i < units; ++i)
     unit_amount /= 1024.0;
 
-  wchar_t tmp[64];
-  // If the first decimal digit is 0, don't show it.
-  double int_part;
-  double fractional_part = modf(unit_amount, &int_part);
-  modf(fractional_part * 10, &int_part);
-  if (int_part == 0) {
-    base::swprintf(tmp, arraysize(tmp),
-                   L"%lld", static_cast<int64>(unit_amount));
-  } else {
-    base::swprintf(tmp, arraysize(tmp), L"%.1lf", unit_amount);
-  }
+  wchar_t buf[64];
+  if (bytes != 0 && units != DATA_UNITS_BYTE && unit_amount < 100)
+    base::swprintf(buf, arraysize(buf), L"%.1lf", unit_amount);
+  else
+    base::swprintf(buf, arraysize(buf), L"%.0lf", unit_amount);
 
-  std::wstring ret(tmp);
+  std::wstring ret(buf);
   if (show_units) {
     ret += L" ";
     ret += suffix[units];
diff --git a/base/string_util_unittest.cc b/base/string_util_unittest.cc
index 8fc8f15..4602344 100644
--- a/base/string_util_unittest.cc
+++ b/base/string_util_unittest.cc
@@ -362,20 +362,32 @@ TEST(StringUtilTest, FormatBytes) {
     const wchar_t* expected;
     const wchar_t* expected_with_units;
   } cases[] = {
+    // Expected behavior: we show one post-decimal digit when we have
+    // under two pre-decimal digits, except in cases where it makes no
+    // sense (zero or bytes).
+    // Since we switch units once we cross the 1000 mark, this keeps
+    // the display of file sizes or bytes consistently around three
+    // digits.
     {0, DATA_UNITS_BYTE, L"0", L"0 B"},
     {512, DATA_UNITS_BYTE, L"512", L"512 B"},
     {512, DATA_UNITS_KIBIBYTE, L"0.5", L"0.5 kB"},
     {1024*1024, DATA_UNITS_KIBIBYTE, L"1024", L"1024 kB"},
-    {1024*1024, DATA_UNITS_MEBIBYTE, L"1", L"1 MB"},
-    {1024*1024*1024, DATA_UNITS_GIBIBYTE, L"1", L"1 GB"},
-    {10LL*1024*1024*1024, DATA_UNITS_GIBIBYTE, L"10", L"10 GB"},
+    {1024*1024, DATA_UNITS_MEBIBYTE, L"1.0", L"1.0 MB"},
+    {1024*1024*1024, DATA_UNITS_GIBIBYTE, L"1.0", L"1.0 GB"},
+    {10LL*1024*1024*1024, DATA_UNITS_GIBIBYTE, L"10.0", L"10.0 GB"},
+    {99LL*1024*1024*1024, DATA_UNITS_GIBIBYTE, L"99.0", L"99.0 GB"},
+    {105LL*1024*1024*1024, DATA_UNITS_GIBIBYTE, L"105", L"105 GB"},
+    {105LL*1024*1024*1024 + 500LL*1024*1024, DATA_UNITS_GIBIBYTE,
+     L"105", L"105 GB"},
     {~(1LL<<63), DATA_UNITS_GIBIBYTE, L"8589934592", L"8589934592 GB"},
-    // Make sure the first digit of the fractional part works.
-    {1024*1024 + 103, DATA_UNITS_KIBIBYTE, L"1024.1", L"1024.1 kB"},
+
+    {99*1024 + 103, DATA_UNITS_KIBIBYTE, L"99.1", L"99.1 kB"},
+    {1024*1024 + 103, DATA_UNITS_KIBIBYTE, L"1024", L"1024 kB"},
     {1024*1024 + 205 * 1024, DATA_UNITS_MEBIBYTE, L"1.2", L"1.2 MB"},
     {1024*1024*1024 + (927 * 1024*1024), DATA_UNITS_GIBIBYTE,
      L"1.9", L"1.9 GB"},
-    {10LL*1024*1024*1024, DATA_UNITS_GIBIBYTE, L"10", L"10 GB"},
+    {10LL*1024*1024*1024, DATA_UNITS_GIBIBYTE, L"10.0", L"10.0 GB"},
+    {100LL*1024*1024*1024, DATA_UNITS_GIBIBYTE, L"100", L"100 GB"},
 #ifdef NDEBUG
     {-1, DATA_UNITS_BYTE, L"", L""},
 #endif