Why do I get different results when compiling the same code with different ide?

Question

I have a basic code about reading true rms.I compiled the same code with arduino ide and atmel studio, then ran it in a proteus simulation.I'm trying to measure how long the read_rms() function takes.

My mcu:attiny84

1.experiment)I have added board to arduino ide with board manager.And I chose attiny84 and internal 1Mhz from tools menu in arduino menu. The result was that the read_rms() function took 23.25 milliseconds.

2.experiment)I compiled the same code without any changes in Atmel Studio.Device,attiny84 selected. The result was that the read_rms() function took 44 milliseconds.

44 miliseconds vs 23.25 miliseconds. Why?

Note:The following settings are selected in the proteus.Internal RC Osc. 8 Mhz,and CKDIV8=Programmed.

My code:

#define F_CPU 1000000UL
#include <avr/io.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <stdint.h>   
const uint8_t muxbits = 1<<MUX3 | 1<<MUX2 | 1<<MUX1 | 1<<MUX0;   


void adc_init()
{
    ADMUX = 0;    //Vcc_ref_
    ADCSRA = (1<<ADEN)|(1<<ADPS1)|(1<<ADPS0); //adc_enable_and_prescaler_8_ 125000 Hz (1000000/8)
    //first_try
    ADCSRA |= (1<<ADSC);
    while ((ADCSRA & (1<<ADSC)) != 0);
}

uint16_t adc_read(uint8_t channel)  
{
    ADMUX = (ADMUX & ~muxbits) | channel;
    // start_single_convertion
    ADCSRA |= (1<<ADSC);
    
    // wait for conversion to complete
    while ((ADCSRA & (1<<ADSC)) != 0);
    
    return (ADC);
}
   
double read_rms()
{
    uint16_t i=0;
    uint16_t a_data=0;
    uint32_t sum=0;
    float avarage=0;
    double rms=0;
    for(i=0;i<200;i++)
    {
        a_data=adc_read(1);
        
        sum=sum+(a_data*a_data);
    }
    avarage=(float)sum/200;
    rms=sqrt((double)avarage);
    
    
    return rms;
    
}


int main(void)
{
    
    DDRA|=(1<<7);
    PORTA &=~ (1<<7);       
    adc_init();

    while(1)
    {

    read_rms();    
    PORTA ^= (1<<7);// TOOGLE_PA7   for_measure_time_of_read_rms()_with_oscilloscope
        
    }
}

Answer 1

Different compilers produce different machine code.

As Majenko pointed out, the Arduino IDE's compiler, which happens to be GCC, uses float even when you write double.

The Atmel Studio creates double for double, using twice as much bits.

Calculating with more bits takes longer.