Module platform 

Hardware pointer masking platform detection and operations.

Supports:

• ARM64 TBI (Top Byte Ignore): Always available on ARM64. Hardware ignores the top byte of pointers, giving us 8 bits for GC metadata.
• x86-64 LAM (Linear Address Masking): Available on recent Intel/AMD. Masks bits 62:57 (LAM57) or 62:48 (LAM48).
• Software fallback: Manually AND-mask before dereferencing.

Pointer format

ARM TBI:     [COLOR:2][GEN:1][unused:5][ADDRESS:56]
x86-64 LAM:  [0][COLOR:2][GEN:1][unused:3][ADDRESS:57]
Fallback:    Same format, software AND mask before deref

Integration with NaN-boxing

NaN-boxing uses a 48-bit PAYLOAD_MASK which already strips upper bits. GC metadata lives in bits 48-55 which are zeroed by PAYLOAD_MASK. So existing ValueWord pointer extraction automatically strips GC tags. Tags are only relevant inside the GC itself.

Enums

MaskingMode

Detected pointer masking mode.

Functions

cached_masking_mode

Get the cached masking mode, detecting on first call.

detect_masking_mode

Detect the best available pointer masking mode for this platform.

has_x86_lam

Check if x86-64 LAM is available (runtime-detected).

mask_ptr

Strip metadata bits from a tagged pointer, returning the raw address.

read_color

Read the color from a tagged pointer.

read_generation

Read the generation from a tagged pointer.

tag_ptr

Tag a raw pointer with GC metadata (color and generation).