CPUID(leaf, subleaf, register-index)

Returns a 32-bit register value from the CPU’s CPUID instruction.

leaf (EAX input) selects the query (e.g., feature flags, topology).
subleaf (ECX input) refines the query for some leaves (set to 0 if unused).
register-index chooses which returned register to read:

Value	Register
0	EAX
1	EBX
2	ECX
3	EDX

If register-index is outside 0–3, an error is raised.

For a survey of leaves/subleaves and their meanings, see the cpuid command’s reference.

Examples

REM Print the highest supported standard leaf
max_leaf = CPUID(&00000000, 0, 0)  REM EAX
PRINT "Max standard leaf = "; max_leaf

REM Detect SSE2 (leaf 1, EDX bit 26)
features_edx = CPUID(&00000001, 0, 3)
IF BITAND(features_edx, &04000000) <> 0 THEN
    PRINT "SSE2 supported"
ELSE
    PRINT "SSE2 NOT supported"
ENDIF

REM Detect AVX (leaf 1, ECX bit 28) and OSXSAVE (leaf 1, ECX bit 27)
features_ecx = CPUID(&00000001, 0, 2)
has_osxsave = BITAND(features_ecx, &08000000)    <> 0  REM bit 27
has_avx     = BITAND(features_ecx, &10000000)    <> 0  REM bit 28
IF has_osxsave = TRUE THEN
    IF has_avx = TRUE THEN
        PRINT "AVX supported (CPU advertises AVX and OSXSAVE)"
    ELSE
        PRINT "No AVX (CPU missing AVX bit)"
    ENDIF
ELSE
    PRINT "No AVX usable (OSXSAVE not set)"
ENDIF

REM Detect BMI2 (leaf 7 subleaf 0, EBX bit 8)
ebx_7_0 = CPUID(&00000007, 0, 1)
IF BITAND(ebx_7_0, &00000100) <> 0 THEN
    PRINT "BMI2 supported"
ELSE
    PRINT "BMI2 NOT supported"
ENDIF

REM Print the highest supported extended leaf
max_ext = CPUID(&80000000, 0, 0)  REM EAX
PRINT "Max extended leaf = "; max_ext

Notes

Return width: The function returns a Retro Rocket integer (64-bit signed), but only the low 32 bits are meaningful; the result is the raw register value.
Signed vs unsigned: Some feature bits set the high bit; if you print the value as a signed decimal it may appear negative. Use hex masks (e.g., &10000000) with BITAND in tests, as shown in the examples.
Subleaf usage: Many leaves ignore subleaf; pass 0 unless the leaf explicitly defines subleaf semantics (e.g., leaves &00000004, &0000000B, &00000007, &8000001D, etc.).
Determinism: CPUID serialises certain execution on many CPUs and is safe to call at any time from BASIC programs. It has no side effects in Retro Rocket.
Platform baseline: Retro Rocket targets x86-64 where CPUID is available. No compatibility shim is provided for pre-CPUID 80386/early 80486 systems.
Reading multi-word strings: Some CPUID leaves (e.g., brand string at &80000002..&80000004) return packed ASCII in four registers per leaf. CPUID gives you the raw 32-bit words; if you wish to render them as text, extract bytes with bit masks and compose characters with CHR$. (Feature bit probing, as above, is usually what you want inside BASIC.)

See also: BITAND · BITOR · BITNAND · cpuid (command)