Rewrite Meter_humanUnit() to accept floating point value

Since Meter_humanUnit() is often called with floating point values in
Meter objects, rewrite the function to let it process `double` type
natively, and save floating point to integer casts.

The rewritten function:
* Allows higher orders of magnitude including 'R' and 'Q', and
  addresses infinity. (The previous version has a maximum value of
  (2^64 - 1) representing 16 ZiB.)
* Rounds values when they are in intervals (99.9, 100) and (9.99, 10),
  and displays them with correct precision (number of fraction digits).
* Produces assertion error on negative and NaN values (undefined
  behavior).

Signed-off-by: Kang-Che Sung <explorer09@gmail.com>

4 files changed, 43 insertions, 30 deletions

diff --git a/Meter.c b/Meter.c
index 12c8c941..64e88071 100644
--- a/Meter.c
+++ b/Meter.c
@@ -51,32 +51,40 @@ Meter* Meter_new(const Machine* host, unsigned int param, const MeterClass* type
    return this;
 }
 
-int Meter_humanUnit(char* buffer, unsigned long int value, size_t size) {
-   const char* prefix = "KMGTPEZY";
-   unsigned long int powi = 1;
-   unsigned int powj = 1, precision = 2;
-
-   for (;;) {
-      if (value / 1024 < powi)
-         break;
-
-      if (prefix[1] == '\0')
+/* Converts 'value' in kibibytes into a human readable string.
+   Example output strings: "0K", "1023K", "98.7M" and "1.23G" */
+int Meter_humanUnit(char* buffer, double value, size_t size) {
+   size_t i = 0;
+
+   assert(value >= 0.0);
+   while (value >= ONE_K) {
+      if (i >= ARRAYSIZE(unitPrefixes) - 1) {
+         if (value > 9999.0) {
+            return snprintf(buffer, size, "inf");
+         }
          break;
+      }
 
-      powi *= 1024;
-      ++prefix;
+      value /= ONE_K;
+      ++i;
    }
 
-   if (*prefix == 'K')
-      precision = 0;
+   int precision = 0;
 
-   for (; precision > 0; precision--) {
-      powj *= 10;
-      if (value / powi < powj)
-         break;
+   if (i > 0) {
+      // Fraction digits for mebibytes and above
+      precision = value <= 99.9 ? (value <= 9.99 ? 2 : 1) : 0;
+
+      // Round up if 'value' is in range (99.9, 100) or (9.99, 10)
+      if (precision < 2) {
+         double limit = precision == 1 ? 10.0 : 100.0;
+         if (value < limit) {
+            value = limit;
+         }
+      }
    }
 
-   return snprintf(buffer, size, "%.*f%c", precision, (double) value / powi, *prefix);
+   return snprintf(buffer, size, "%.*f%c", precision, value, unitPrefixes[i]);
 }
 
 void Meter_delete(Object* cast) {
diff --git a/Meter.h b/Meter.h
index e0ca1f07..6b14634a 100644
--- a/Meter.h
+++ b/Meter.h
@@ -146,7 +146,9 @@ extern const MeterClass Meter_class;
 
 Meter* Meter_new(const Machine* host, unsigned int param, const MeterClass* type);
 
-int Meter_humanUnit(char* buffer, unsigned long int value, size_t size);
+/* Converts 'value' in kibibytes into a human readable string.
+   Example output strings: "0K", "1023K", "98.7M" and "1.23G" */
+int Meter_humanUnit(char* buffer, double value, size_t size);
 
 void Meter_delete(Object* cast);
 
diff --git a/XUtils.h b/XUtils.h
index cfb375cc..afe22112 100644
--- a/XUtils.h
+++ b/XUtils.h
@@ -111,4 +111,7 @@ int compareRealNumbers(double a, double b);
    nonnegative. */
 double sumPositiveValues(const double* array, size_t count);
 
+/* IEC unit prefixes */
+static const char unitPrefixes[] = { 'K', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y', 'R', 'Q' };
+
 #endif
diff --git a/pcp/PCPDynamicMeter.c b/pcp/PCPDynamicMeter.c
index 241153a0..1e118351 100644
--- a/pcp/PCPDynamicMeter.c
+++ b/pcp/PCPDynamicMeter.c
@@ -351,27 +351,27 @@ void PCPDynamicMeter_updateValues(PCPDynamicMeter* this, Meter* meter) {
             break;
          case PM_TYPE_32:
             bytes += conv.dimSpace ?
-               Meter_humanUnit(buffer + bytes, atom.l, size - bytes) :
+               Meter_humanUnit(buffer + bytes, (double) atom.l, size - bytes) :
                xSnprintf(buffer + bytes, size - bytes, "%d", atom.l);
             break;
          case PM_TYPE_U32:
             bytes += conv.dimSpace ?
-               Meter_humanUnit(buffer + bytes, atom.ul, size - bytes) :
+               Meter_humanUnit(buffer + bytes, (double) atom.ul, size - bytes) :
                xSnprintf(buffer + bytes, size - bytes, "%u", atom.ul);
             break;
          case PM_TYPE_64:
             bytes += conv.dimSpace ?
-               Meter_humanUnit(buffer + bytes, atom.ll, size - bytes) :
+               Meter_humanUnit(buffer + bytes, (double) atom.ll, size - bytes) :
                xSnprintf(buffer + bytes, size - bytes, "%lld", (long long) atom.ll);
             break;
          case PM_TYPE_U64:
             bytes += conv.dimSpace ?
-               Meter_humanUnit(buffer + bytes, atom.ull, size - bytes) :
+               Meter_humanUnit(buffer + bytes, (double) atom.ull, size - bytes) :
                xSnprintf(buffer + bytes, size - bytes, "%llu", (unsigned long long) atom.ull);
             break;
          case PM_TYPE_FLOAT:
             bytes += conv.dimSpace ?
-               Meter_humanUnit(buffer + bytes, atom.f, size - bytes) :
+               Meter_humanUnit(buffer + bytes, (double) atom.f, size - bytes) :
                xSnprintf(buffer + bytes, size - bytes, "%.2f", (double) atom.f);
             break;
          case PM_TYPE_DOUBLE:
@@ -427,27 +427,27 @@ void PCPDynamicMeter_display(PCPDynamicMeter* this, ATTR_UNUSED const Meter* met
             break;
          case PM_TYPE_32:
             len = conv.dimSpace ?
-               Meter_humanUnit(buffer, atom.l, sizeof(buffer)) :
+               Meter_humanUnit(buffer, (double) atom.l, sizeof(buffer)) :
                xSnprintf(buffer, sizeof(buffer), "%d", atom.l);
             break;
          case PM_TYPE_U32:
             len = conv.dimSpace ?
-               Meter_humanUnit(buffer, atom.ul, sizeof(buffer)) :
+               Meter_humanUnit(buffer, (double) atom.ul, sizeof(buffer)) :
                xSnprintf(buffer, sizeof(buffer), "%u", atom.ul);
             break;
          case PM_TYPE_64:
             len = conv.dimSpace ?
-               Meter_humanUnit(buffer, atom.ll, sizeof(buffer)) :
+               Meter_humanUnit(buffer, (double) atom.ll, sizeof(buffer)) :
                xSnprintf(buffer, sizeof(buffer), "%lld", (long long) atom.ll);
             break;
          case PM_TYPE_U64:
             len = conv.dimSpace ?
-               Meter_humanUnit(buffer, atom.ull, sizeof(buffer)) :
+               Meter_humanUnit(buffer, (double) atom.ull, sizeof(buffer)) :
                xSnprintf(buffer, sizeof(buffer), "%llu", (unsigned long long) atom.ull);
             break;
          case PM_TYPE_FLOAT:
             len = conv.dimSpace ?
-               Meter_humanUnit(buffer, atom.f, sizeof(buffer)) :
+               Meter_humanUnit(buffer, (double) atom.f, sizeof(buffer)) :
                xSnprintf(buffer, sizeof(buffer), "%.2f", (double) atom.f);
             break;
          case PM_TYPE_DOUBLE: