issue with fmaf function

[KwA]

Hallo,

I used in my app fmaf function and I found it doesn't behave as expected:

y = fmaf(a1,a2,a3) should be y = a1*a2 + a3

but I got as result y = a1*a2 without additive term.

Of course I can and use "classic" expresion instead this functions.

Is this a bug or maybe I misunderstood something?

I'm using STM32CubeIDE 1.13.2, and STM32F401ceu...

Greg

 

Below is also dissasembled piece of code:

 

137 q = fmaf(0.98564736f, D, 280.459f);
080014ea: vldr s2, [pc, #200] ; 0x80015b4 <Sun_Longitude_Deg+332>
080014ee: vldr s1, [r7, #4]
080014f2: vldr s0, [pc, #188] ; 0x80015b0 <Sun_Longitude_Deg+328>
080014f6: bl 0x800c8d0 <fmaf>

fmaf:
0800c8d0: vfma.f32 s0, s0, s1
0800c8d4: bx lr
0800c8d6: movs r0, r0
__ieee754_atan2:

 

[STTwo-32]

Hello @KwA and welcome to the ST Community :smiling_face_with_smiling_eyes:.

I can't reproduce that issue. Can you share your code here so we may can find the problem.

Best Regards.

STTwo-32 

[KwA]

Hello, yes I can share but I think it is unusable in this form. I just use normal expression insted of fma. This all fma callings are commented out.

Sorry, the code looks terrible - I don't know how to make this formated here:

 

float Sun_Longitude_Deg(float D) {
float g, q, L;
float gr;

// g, q, and L are in degrees
// Mean anomaly of the Sun:
g = 357.529f + 0.98560028f * D;
//g = fmaf(0.98560028f , D, 357.529f);

if (g >= 360) //while (g > 360)
{ //g -= 360;
g = fmodf(g, 360);
} else {
while (g < 0) { g += 360;}
}

// Mean longitude of the Sun:
q = 280.459f + 0.98564736f * D;
//q = fmaf(0.98564736f, D, 280.459f);
if (q >= 360) //while (q > 360)
{ //q -= 360;
q = fmodf(q, 360);
} else {
while (q < 0) { q += 360;}
}

// Sun's geocentric apparent ecliptic longitude (adjusted for aberration):

gr = D2R(g);
L = q + 1.915f*sinf(gr) + 0.020f*sinf(2*gr);

//L = fmaf(1.915f, sinf(gr), q);
//L = fmaf(0.020f, sinf(2*gr), L);

return L;
}

[Tesla DeLorean]

Yes looks broken, although the Keil output has __hardfp_fmap which is much more complex

 0x08003eda: ed9f0a0c .... VLDR s0,[pc,#48] ; [0x8003f0c] = 0x3f7c5363
 0x08003ede: eddf0a0c .... VLDR s1,[pc,#48] ; [0x8003f10] = 0x42f6e666
 0x08003ee2: ed9f1a0c .... VLDR s2,[pc,#48] ; [0x8003f14] = 0x438c3ac1
 0x08003ee6: f000f829 ..). BL __hardfp_fmaf ; 0x8003f3c

 

[Tesla DeLorean]

With GNU 4.93 something similar

f = fmaf(0.98564736f, f, 280.459f);

 0x080015e4: ed9d7a02 ...z VLDR s14,[sp,#8]
 0x080015e8: eddf6a23 ..#j VLDR s13,[pc,#140] ; [0x8001678] = 0x3f7c5363
 0x080015ec: eddf7a23 ..#z VLDR s15,[pc,#140] ; [0x800167c] = 0x438c3ac1
 0x080015f0: 481b .H LDR r0,[pc,#108] ; [0x8001660] = 0x80084ef
 0x080015f2: eee67a87 ...z VFMA.F32 s15,s13,s14
 0x080015f6: edcd7a02 ...z VSTR s15,[sp,#8]

 printf("%f\n", f);

 0x080015fa: eddd7a02 ...z VLDR s15,[sp,#8]
 0x080015fe: eeb77ae7 ...z VCVT.F64.F32 d7,s15
 0x08001602: ec532b17 S..+ VMOV r2,r3,d7
 0x08001606: f002fb81 .... BL printf ; 0x8003d0c

[KwA]

in this dissasembly it looks like VFMA is operating on three different registers contrary to my where it operates on two different registers (omits s2 in my case).