zaaath commented on code in PR #2977:
URL: https://github.com/apache/cassandra/pull/2977#discussion_r1424378757
##########
src/java/org/apache/cassandra/utils/FBUtilities.java:
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@@ -939,6 +939,33 @@ public static String prettyPrintMemory(long size, String
separator)
UNIT_PREFIXES.charAt(UNIT_PREFIXES_BASE +
prefixIndex));
}
+ /**
+ * Convert the given size in bytes to a human-readable value using binary
(i.e. 2^10-based) modifiers
+ * with only three significant digits.
+ * For example, "4.96 KiB", "48.8 KiB", "477 MiB", "0.422 KiB", "0.000
KiB".
+ * @param size Number to convert.
+ */
+ public static String prettyPrintMemoryShort(long size)
Review Comment:
yeah, it is hard to follow. I tried my best to streamline the logic. Let me
know if there is more I can do.
This is actually similar to the existing `FBUtilities#prettyPrintMemory`
method with some additional logic for keeping only the first three significant
digits.
"Line-by-line" explanation:
1. Calculate Prefix Index: `int prefixIndex = (63 -
Long.numberOfLeadingZeros(Math.abs(size))) / 10;` determines the appropriate
prefix (like Kilo, Mega, Giga, etc.) for the given size. It calculates how many
bits are needed to represent the absolute value of `size`, then divides this by
10 to find the index in the `UNIT_PREFIXES` string.
2. Adjust for Smallest Prefix: `if (prefixIndex == 0) prefixIndex = 1;`
ensures that for sizes less than 1024 bytes (where `prefixIndex` would be 0),
the 'Kilo' prefix is used instead.
3. Get Prefix Character: `char prefix =
UNIT_PREFIXES.charAt(UNIT_PREFIXES_BASE + prefixIndex);` retrieves the
corresponding unit prefix character from UNIT_PREFIXES string based on the
prefixIndex.
4. Scale the Size: `float scaledSize = Math.scalb(size, -prefixIndex * 10);`
scales the size down by the factor determined by the prefix index. This is
effectively dividing the size by 2^(10×prefixIndex).
5. Format Scaled Size: The block of code after `String scaledSizeStr;`
formats the scaled size to have only three significant digits. It checks if the
scaled size is between -1 and 1 (not inclusive) and simply calls
`String.format` on it; otherwise, it calculates how many decimal places to
include to ensure only three significant digits, after which calls
`String.format` on it.
6. Merge Scaled Size with Prefix. `return String.format` constructs the
final string representing the size in a human-readable format, appending the
appropriate unit prefix and the suffix 'iB' for binary unit.
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