Graphics on BangleJS2

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•

Gordon

I was hoping I could add the following to E.compiledC, but even after accounting for the double-escaping, I'm not having success :

float __attribute__((naked)) __aeabi_d2f(double d) {__asm__ volatile(
    "lsrs r0, #30\n\t"
    "lsls r2, r1, #12\n\t"
    "lsrs r2, #9\n\t"
    "asrs r1, #22\n\t"
    "lsls r1, #22\n\t"
    "orrs r0, r1\n\t"
    "orrs r0, r2\n\t"
    "bx lr"
);}

double __attribute__((naked)) __aeabi_f2d(float f) {__asm__ volatile(
    "asrs r1, r0, #3\n\t"
    "movs r2, [#0xf](https://forum.espruino.com/search/?q=%230xf)\n\t"
    "lsls r2, #27\n\t"
    "orrs r1, r2\n\t"
    "lsls r0, #25\n\t"
    "bx lr"
);}

If you have any luck, please let me know!

•

fanoush in reply to @Gordon

Currently you can pass single precision floats (and converted doubles) into inline C code and back via Float32Array or with shared buffer with Int32Array for conversions of single values when passing parameters (more info https://gist.github.com/fanoush/9227640a869d78d69a799276dff0fb71#file-espruino-fpu-softfp-inlinec-js-L24), maybe it would be nice to support float type directly when passing parameters to native code (with automatic conversion to/from javascript double)? then d2f and f2d would not be needed?

•

FManga in reply to @Gordon

The Pico code is for a Cortex M0+ and what you have in your snippet is incomplete.
The correct code for a Cortex M4 is this (from assembled+disassembled libgcc, corrected to return the result in S0 instead of R0, since the compiler ignores the softfp ABI for functions in the same compilation unit, apparently):

let c = E.compiledC(`
// int boop(double)

extern "C" float __attribute__((naked)) d2f(double) {__asm__ volatile(R"(
 	mov.w	r2, r1, lsl 1
 	subs.w	r3, r2, 0x70000000
 	itt	cs
 	subscs.w ip, r3, 0x200000
 	rsbscs	ip, ip, 0x1fc00000
 	bls.n	2f
1:
 	and.w	ip, r1, 0x80000000
 	mov.w	r2, r0, lsl 3
 	orr.w	r0, ip, r0, lsr 29
 	cmp.w	r2, 0x80000000
 	adc.w	r0, r0, r3, lsl 2
 	it	eq
 	biceq.w	r0, r0, 1
 	b 6f
2:
 	tst.w	r1, 0x40000000
 	bne.n	3f
 	adds.w	r2, r3, 0x2e00000
 	itt	lt
 	andlt.w	r0, r1, 0x80000000
 	blt	6f
 	orr.w	r1, r1, 0x100000
 	mov.w	r2, r2, lsr 21
 	rsb	r2, r2, 24
 	rsb	ip, r2, 32
 	lsls.w	r3, r0, ip
 	lsr.w	r0, r0, r2
 	it	ne
 	orrne.w	r0, r0, 1
 	mov.w	r3, r1, lsl 11
 	mov.w	r3, r3, lsr 11
 	lsl.w	ip, r3, ip
 	orr.w	r0, r0, ip
 	lsr.w	r3, r3, r2
 	mov.w	r3, r3, lsl 1
 	b.n	1b
3:
 	mvns.w	r3, r2, asr 21
 	bne.n	5f
 	orrs.w	r3, r0, r1, lsl 12
 	ittt	ne
 	movne.w	r0, 0x7f000000
 	orrne.w	r0, r0, 0xc00000
 	bne	6f
5:
 	and.w	r0, r1, 0x80000000
 	orr.w	r0, r0, 0x7f000000
 	orr.w	r0, r0, 0x800000
6:
  vmov s0, r0
 	bx	lr
 	nop
)");}


int boop(double d) {
  return d2f(d) * 3;
}
`);

print('boop:', c.boop(3.5)); // 3.5 * 3 = 10.5 cast to int = 10

Note that you have to call the function explicitly, I couldn't use a float cast and get it to link as __aeabi_d2f. It might work if we compile the assembly into a library and then link to that. If one were to go that far, might as well link to libgcc and let the linker throw away all the stuff that isn't used.

Graphics on BangleJS2

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