php-in-php: fpow() early registration — align #4605 with VmMath, version gate, and IEEE edge cases

[PurHur]

Category

stdlib | php-in-PHP

Problem

#4605 was filed when fpow() was entirely missing. Audit (2026-06-06): VM now registers fpow() (function_exists('fpow') → true, fpow(2,3) → 8) while the open issue still describes undefined-function failure.

Remaining gaps vs php-src ext/standard/math.c PHP_FUNCTION(fpow):

1. Version gate — exposed on CompilerVersion 8.3.0-dev before PHP 8.4 target alignment
2. IEEE edge cases — fpow(-1, 0.5) → NAN, fpow(0, -1) → INF, signed-zero exponent rules
3. TypeError paths — non-numeric operands (Z_PARAM_DOUBLE), enum case operands (php-src-strict)
4. JIT/AOT — may still defer; capability matrix must reflect reality
5. Implementation location — ensure logic lives in ext/standard/VmMath.php / fpow.php, not ad-hoc C

php-src reference

• php/php-src ext/standard/math.c — PHP_FUNCTION(fpow)
• php/php-src ext/standard/basic_functions.c — PHP 8.4+ registration

Repro

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php bin/vm.php -r "var_export(function_exists(\"fpow\")); echo PHP_EOL; var_export(fpow(2,3)); echo PHP_EOL; var_export(fpow(-1,0.5)); echo PHP_EOL;"
php -r "var_export(function_exists(\"fpow\")); echo PHP_EOL;" 2>/dev/null || echo zend_pre_84
'

Check	Expected (Zend 8.4+)	VM today
function_exists('fpow')	true (8.4+)	true (early)
fpow(2,3)	8.0	8 ✅
fpow(-1,0.5)	NAN	verify ❓
Enum case arg	TypeError	verify ❓

Scope

Path	Work
ext/standard/fpow.php / VmMath.php	centralize libc pow() + edge cases
lib/CompilerVersion.php	supportsFpow() ≥ 8.4
lib/JIT/	native double pow lowering (phase 2)
#4605	close or rewrite when this lands
Tests	test/compliance/cases/stdlib/fpow*.phpt

No new runtime/*.c math helpers.

Done when

• Behavior matrix matches Zend 8.4 for happy + edge cases
• CompilerVersion gate prevents fpow on pre-8.4 target if required by project policy
• php-src-strict enum/object operand rejection on VM (+ JIT when lowered)
• Stdlib: fpow() — IEEE-754 exponentiation (ext/standard/math.c, PHP 8.4) #4605 updated/closed; capability matrix row accurate (VM yes / JIT status)
• ./script/ci-fast.sh --filter fpow green

Related

• Stdlib: fpow() — IEEE-754 exponentiation (ext/standard/math.c, PHP 8.4) #4605 (original missing-function spec — stale) · Stdlib: fdiv() — numeric-string coercion + TypeError parity (ext/standard/math.c) #4388 fdiv() pattern · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

claim: PHP Runtime → PHP — starting this run (#7045: VmMath::fpow(), CompilerVersion::supportsFpow(), remove host \fpow() dependency).

[PurHur]

Merged via #7622

PHP path: VmMath::fpow() in ext/standard/VmMath.php; ext/standard/fpow.php no longer calls host \\fpow(). CompilerVersion::supportsFpow() gates registration in Module.php.

C shrink: 0 lines (no runtime/ changes).

Verification (green): ./vendor/bin/phpunit --filter fpow — VM+JIT compliance for basic, edge (INF/NAN), and enum TypeError (6/7; AOT fpow_basic still fails pre-existing harness LLVM verify, not fpow-specific).