Improve conversion of bytes to human readable string

Fixes issues like showing 0 MiB when the value is just slightly less then 1 MiB.

pglablib/utils/HumanReadableBytes.cpp

@@ -0,0 +1,56 @@
+#include "HumanReadableBytes.h"
+#include <iomanip>
+#include <sstream>
+
+using namespace std;
+
+namespace {
+
+struct scale {
+    int64_t scale;
+    const char* prefix;
+};
+
+void fmt(std::ostringstream &o, double d)
+{
+    ;
+    if (d < 10.0)
+    {
+        o << fixed << setprecision(2) << d;
+        //return std::format("{:.3g}", d);
+    }
+    else if (d < 100.0)
+    {
+        o << fixed << setprecision(1) << d;
+        //return std::format("{:.3g}", d);
+    }
+    else
+    {
+        o << fixed << setprecision(0) << d;
+    }
+}
+
+}
+
+std::string HumanReadableBytes(uint64_t bytes)
+{
+    static scale scales[] = {
+                             { 1024ll * 1024 * 1024 * 1024, "Ti" },
+                             { 1024ll * 1024 * 1024, "Gi" },
+                             { 1024ll * 1024, "Mi" },
+                             { 1024ll, "ki" },
+                             };
+
+    std::ostringstream out;
+    for (int i = 0; i < (sizeof(scales) / sizeof(scale)); ++i)
+    {
+        if (bytes >= scales[i].scale)
+        {
+            fmt(out, bytes / double(scales[i].scale));
+            out << " " << scales[i].prefix << "B";
+            return out.str();
+        }
+    }
+    out << bytes << " B";
+    return out.str();
+}