vigneshshanmugam / elements-kinds Goto Github PK

The current containsHoles implementation seems to check for undefined values:

Holes are something else, though!

• [undefined, undefined, undefined] is a packed array that happens to contain undefined values.
• Examples of holey arrays are [1,,2], x = [1, 2, 3]; delete x[1], new Array(10), and x = []; x[42] = 1.

You can detect holes by using the in operator, or by using hasOwnProperty.

isSMI currently uses Number.isMaxSafeInteger which goes all the way to 2**53-1:

However, the actual Smi range is Signed31 on 32-bit architectures and Signed32 on 64-bit architectures. Since the last bit is used to distinguish positive and negative numbers, that leaves 30 or 31 bits for the actual numeric value, respectively.

On my machine (64-bit):

%DebugPrint([2**31-1]);
// → PACKED_SMI_ELEMENTS
%DebugPrint([2**31]);
// → PACKED_DOUBLE_ELEMENTS

isDouble just checks for numbers:

This appears to work fine because of the ordering used here, where isDouble is only used if it’s not an array of Smis:

Suggested fix: either rename isDouble to isNumber, or actually check for double values :)