The inlined `value < 0.0f || value > 1.0f` check in the clamp loop costs
~50 B per iteration on ESP8266 (two libgcc soft-float calls with register
spills). IEEE 754 floats in [0.0f, 1.0f] have bit patterns in
[0x00000000, 0x3F800000]; anything out of range — values > 1.0f, negatives
(sign bit set → huge unsigned interpretation), NaN, Infinity — has a
strictly larger unsigned interpretation. A single `pun.u > 0x3F800000u`
covers every case.
Using a union for the type-pun rather than memcpy/bit_cast because those
don't optimize to a no-op on xtensa-gcc (same reason api/proto.h's
float_to_raw() uses a union).
The loop body is now two instructions for the range check:
l32i a2, a9, 0 ; load raw u32
bgeu a10, a2, ... ; compare against pre-hoisted 1.0f bits
Size delta vs. the prior float-compare form:
ESP32-IDF: validate_ -16 B, net -12 B
ESP8266: validate_ -20 B, net -20 B
vs. dev baseline (isolated light build, matched funcs):
ESP32-IDF: -103 B code, +32 B PROGMEM table = -71 B net
ESP8266: -42 B code, +32 B PROGMEM table = -10 B net
Follow-up to edb2145a addressing three points:
1. Hoist the in-range check out of the logging helper. The loop now tests
`value < 0.0f || value > 1.0f` inline and only calls the out-of-line
log_out_of_range_and_clamp_ helper on the cold path. Hot path (value in
range) skips the call8 and the register spill/reload around it, which
matters because HA automations can drive perform() at high frequency.
2. Iterate only set bits with __builtin_ctz + (active & active-1). Common
calls with one or two flags set now exit the loop after one or two
iterations instead of always scanning all eight slots.
3. Replace the uint8_t* pointer arithmetic with typed float arrays aliasing
&brightness_ in each struct. Per-field static_asserts (expanded via a
local macro) now catch reorders of any single member in either struct,
not just reorders at the endpoints. Compiles to the same machine code as
the uint8_t* version.
Size delta vs. prior commit (isolated light build):
ESP32-IDF: validate_ +60 B, helper -29 B, net +31 B
ESP8266: validate_ +72 B, helper -42 B, net +30 B
Still a net win vs. dev on both targets (ESP32-IDF -91 B, ESP8266 -22 B).
Reorder FieldFlags so the eight [0.0, 1.0]-clamped float fields occupy
bits 0-7 in the same order as they appear in LightCall and
LightColorValues, and move color_temperature_ to the end of both
structs. Under that layout the LightCall offset for clamp field i is
`offsetof(LightCall, brightness_) + i * 4`, and the LightColorValues
offset is exactly 12 bytes lower for every field. validate_() now
iterates the active clamp bits in a small loop that computes these
offsets from the bit position instead of expanding eight nearly
identical inline blocks via macro.
The field-name PROGMEM pointer is passed to clamp_and_log_if_invalid as
`const LogString *const *`; progmem_read_ptr only runs on the cold
(out-of-range) path, so the hot path performs no flash reads for the
name. The eight invariants the loop relies on (flag-bit layout,
field contiguity, and the constant 12-byte delta) are enforced by
static_asserts so any future reshuffle fails loudly at compile time.
Size deltas for the isolated light component build (vs dev):
ESP32-IDF: -118 B code, +32 B PROGMEM name table = -86 B net
ESP8266: -56 B code, +32 B PROGMEM name table = -24 B net
0 B RAM impact on both targets.
J. Nick Koston