c - 这到底是怎么编译成 4kb 的？

Question

#define F_CPU 1000000

#include <stdint.h>
#include <avr/io.h>
#include <util/delay.h>

const uint8_t sequences[] = {
    0b00000001, 
    0b00000011,
    0b00000110,
    0b00001100,
    0b00011000,
    0b00110000,
    0b00100000,
    0b00110000,
    0b00011000,
    0b00001100,
    0b00000110,
    0b00000011,
    0b00000001,
};

const uint8_t totalSequences = sizeof(sequences) / sizeof(sequences[0]);

int main(void) {
    DDRB = 0b00111111;

    uint8_t i;
    uint8_t b;

    while(1) {
        for(i = 0; i < totalSequences; i++) {
            const uint8_t currentSequence = sequences[i];
            const uint8_t nextSequence = sequences[(i + 1) % totalSequences];

            // blend between sequences
            for(b = 0; b < 100; b++) {
                PORTB = currentSequence;  _delay_us(b);
                PORTB = nextSequence;     _delay_us(100-b);
            }

            _delay_ms(50);
        }
    }

    return 0;
}

这是我的全部程序。当我像下面这样直接设置 PORTB(没有混合)时，编译后的二进制文件是 214 字节。当我包含第二个 for 循环时，我编译的二进制文件超过 4kb。我只有 1kb 的 FLASH 可用，所以我需要把它放在那里。

const uint8_t currentSequence = sequences[i];
const uint8_t nextSequence = sequences[(i + 1) % totalSequences];

//// blend between sequences
//for(b = 0; b < 100; b++) {
//  PORTB = currentSequence;  _delay_us(b);
//  PORTB = nextSequence;     _delay_us(100-b);
//}

PORTB = currentSequence;
PORTB = nextSequence;
_delay_ms(50);

我的工具链是 WINAVR，编译如下:

avr-gcc -Os -mmcu=attiny13 -Wall -std=c99 main.c -o main.out
avr-objcopy -O binary main.out main.bin

我不知道如何反编译二进制文件并查看编译器做了什么，但不管它是什么，它都是错误的。为什么带有内部循环的二进制文件是 4kb，我该如何修复它？

修改后的循环(278 字节):

while(1) {
    for(i = 0; i < totalSequences; i++) {
        const uint8_t currentSequence = sequences[i];
        const uint8_t nextSequence = sequences[(i + 1) % totalSequences];

        // blend between sequences
        for(b = 0; b < 100; b++) {
            int d;
            PORTB = currentSequence;  for(d = 0; d < b; d++,   _delay_us(1));
            PORTB = nextSequence;     for(d = 100; b < d; d--, _delay_us(1));
        }

        _delay_ms(50);
    }
}

Answer 1

除非参数是编译时间常量，否则 delay() 函数会增大代码大小。它也不会延迟带有可变参数的正确时间。