【C】记一次GCC -O3优化效果实测
先上源码。_sw_transceive是重点。我在调试STM32F103单片机SPI外设的时候遇到了问题，它并不能成功驱动我的硬件。为了排除外设操作的问题，我用自己写GPIO的方式实现了强行SPI协议传输，来看看传输的调用是不是对的。
这个函数本身很简短，就是模拟SPI外设的工作效果。通过拨弄SCK针来控制时间，然后写MOSI，读MISO。这个函数只有55行，但它用短循环调用了很多宏和static函数。
static uint32_t _sw_transceive(spi_master_ctrl_p smc, uint32_t txval)
{
int bitcount = smc->dff ? 16 : 8;
int togo = bitcount;
uint32_t rxval = 0;
if(!smc->bitorder) txval = _bit_reorder(txval, bitcount);
if(smc->cpha)
{
if(smc->cpol)
{
while(togo --> 0)
{
_sw_clk_l(smc);
_sw_mosi_out(smc, txval & 1); txval >>= 1;
_sw_clk_h(smc);
rxval = (rxval << 1) | _sw_miso_in(smc);
}
}
else
{
while(togo --> 0)
{
_sw_clk_h(smc);
_sw_mosi_out(smc, txval & 1); txval >>= 1;
_sw_clk_l(smc);
rxval = (rxval << 1) | _sw_miso_in(smc);
}
}
}
else
{
if(smc->cpol)
{
while(togo --> 0)
{
rxval = (rxval << 1) | _sw_miso_in(smc);
_sw_mosi_out(smc, txval & 1); txval >>= 1;
_sw_clk_l(smc);
_sw_clk_h(smc);
}
}
else
{
while(togo --> 0)
{
rxval = (rxval << 1) | _sw_miso_in(smc);
_sw_mosi_out(smc, txval & 1); txval >>= 1;
_sw_clk_h(smc);
_sw_clk_l(smc);
}
}
}
if(smc->bitorder) rxval = _bit_reorder(rxval, bitcount);
return rxval;
}熟悉STM32或SPI协议（以及它在STM32的外设接口）的人都能看出我这个函数是在干啥。
然而当我把它编译出来后，得到的二进制明显相当大——虽然是预料之内。至少直接写外设或者通过bit band写外设都是需要进行绝对地址直接寻址的，而且根据SPI的配置，这里存在这样几个变化的情况：[*]传输单位，是以8bit为单位还是16bit为单位（虽然16bit也不过是一次传输两个8bit而已）
[*]时钟相位CPHA，时钟先变化还是数据先变化
[*]时钟极性CPOL，高电平为闲置还是低电平为闲置
[*]位顺序，高位在前还是低位在前
按照GCC的优化能力，它会把不同的情况组合都拆开，并且会把短循环直接展开。那么我们得到的二进制是什么样的呢？请看IDA图表。
这简直有点复杂……
底下这些小格子是怎么回事呢？
说实话我看不懂。我对ARM汇编不熟。
顺手F5一下看看。
简直好多局部变量，而且后面也是各种“缩进拳”，完全和我写的源代码不一样。GCC的各种逻辑优化和循环展开已经把它变得面目全非了。
unsigned int __fastcall sw_transceive(int a1, unsigned int a2)
{
__int64 v2; // kr00_8
int v3; // r2
unsigned int v4; // r3
signed int v5; // r4
int v6; // r2
int v7; // r6
int v8; // r4
int v9; // lr
int v10; // r2
int v11; // r7
int v12; // r12
int v13; // r10
int v14; // r6
int v15; // r11
signed int v16; // r0
_BOOL4 v17; // r11
signed int v18; // r10
_BOOL4 v19; // r0
signed int v20; // r0
signed int v21; // r3
signed int v22; // r0
signed int v23; // r3
int v24; // r0
signed int v25; // r5
_BOOL4 v26; // r0
signed int v27; // r3
int v28; // r10
signed int v29; // r11
unsigned int result; // r0
unsigned int v31; // r1
unsigned int v32; // r2
unsigned int v33; // r2
unsigned int v34; // r2
unsigned int v35; // r2
unsigned int v36; // r2
unsigned int v37; // r2
unsigned int v38; // r2
unsigned int v39; // r3
int v40; // r11
int v41; // r10
int v42; // r9
int v43; // lr
int v44; // r4
int v45; // r12
int v46; // r2
int v47; // r7
int v48; // r3
signed int v49; // r10
int v50; // r11
signed int v51; // r9
signed int v52; // r5
_BOOL4 v53; // r11
signed int v54; // r0
signed int v55; // r9
signed int v56; // r0
_BOOL4 v57; // r9
int v58; // r10
int v59; // r9
int v60; // r0
_BOOL4 v61; // r10
_BOOL4 v62; // r9
signed int v63; // r11
_BOOL4 v64; // r10
_BOOL4 v65; // r10
_BOOL4 v66; // r10
_BOOL4 v67; // r10
_BOOL4 v68; // r10
_BOOL4 v69; // r10
_BOOL4 v70; // r10
unsigned int v71; // r1
_BOOL4 v72; // r3
int v73; // r3
unsigned int v74; // r2
unsigned int v75; // r2
unsigned int v76; // r2
unsigned int v77; // r2
int v78; // r2
unsigned int v79; // r3
unsigned int v80; // r3
unsigned int v81; // r0
int v82; // r6
int v83; // lr
int v84; // r4
int v85; // r3
int v86; // r12
int v87; // r9
int v88; // r7
int v89; // r10
int v90; // r11
signed int v91; // r9
_BOOL4 v92; // r10
_BOOL4 v93; // r11
bool v94; // zf
signed int v95; // r5
signed int v96; // r9
signed int v97; // r0
signed int v98; // r9
signed int v99; // r0
signed int v100; // r0
signed int v101; // r9
int v102; // r9
_BOOL4 v103; // r9
signed int v104; // r11
unsigned int v105; // r1
signed int v106; // r3
int v107; // lr
int v108; // r6
int v109; // r12
int v110; // r4
int v111; // r7
int v112; // r3
signed int v113; // r10
int v114; // r11
signed int v115; // r9
signed int v116; // r5
_BOOL4 v117; // r11
signed int v118; // r0
signed int v119; // r9
signed int v120; // r0
_BOOL4 v121; // r9
int v122; // r10
int v123; // r9
int v124; // r0
_BOOL4 v125; // r10
_BOOL4 v126; // r9
signed int v127; // r11
_BOOL4 v128; // r10
_BOOL4 v129; // r10
_BOOL4 v130; // r10
_BOOL4 v131; // r10
_BOOL4 v132; // r10
_BOOL4 v133; // r10
_BOOL4 v134; // r10
unsigned int v135; // r1
_BOOL4 v136; // r3
signed int v137; //
int v138; //
_BOOL4 v139; //
int v140; //
signed int v141; //
signed int v142; //
signed int v143; //
signed int v144; //
signed int v145; //
signed int v146; //
signed int v147; //
signed int v148; //
_BOOL4 v149; //
signed int v150; //
_BOOL4 v151; //
v2 = *(_QWORD *)(a1 + 24);
v138 = *(_QWORD *)(a1 + 24) >> 32;
if ( !(_DWORD)v2 )
{
if ( HIDWORD(v2) )
{
v137 = 7;
goto LABEL_6;
}
v3 = a2 & 1;
v4 = a2 >> 1;
v5 = 6;
v137 = 7;
LABEL_30:
a2 = (v4 >> 6) & 1 | 2
* ((v4 >> 5) & 1 | 2
* ((v4 >> 4) & 1 | 2
* ((v4 >> 3) & 1 | 2
* ((v4 >> 2) & 1 | 2
* ((v4 >> 1) & 1 | 2 * (v4 & 1 | 2 * v3))))));
v32 = v4 >> 7;
if ( v5 != 6 )
{
a2 = v32 & 1 | 2 * a2;
v33 = v4 >> 8;
if ( v5 > 7 )
{
a2 = v33 & 1 | 2 * a2;
v34 = v4 >> 9;
if ( v5 > 8 )
{
a2 = v34 & 1 | 2 * a2;
v35 = v4 >> 10;
if ( v5 > 9 )
{
a2 = v35 & 1 | 2 * a2;
v36 = v4 >> 11;
if ( v5 > 10 )
{
a2 = v36 & 1 | 2 * a2;
v37 = v4 >> 12;
if ( v5 > 11 )
{
a2 = v37 & 1 | 2 * a2;
v38 = v4 >> 13;
if ( v5 > 12 )
{
a2 = v38 & 1 | 2 * a2;
v39 = v4 >> 14;
if ( v5 == 14 )
a2 = v39 | 2 * a2;
}
}
}
}
}
}
}
LABEL_6:
v7 = *(_QWORD *)(a1 + 16) >> 32;
v6 = *(_QWORD *)(a1 + 16);
if ( v7 )
goto LABEL_7;
goto LABEL_40;
}
if ( !HIDWORD(v2) )
{
v3 = a2 & 1;
v4 = a2 >> 1;
v5 = 14;
v137 = 15;
goto LABEL_30;
}
v7 = *(_QWORD *)(a1 + 16) >> 32;
v6 = *(_QWORD *)(a1 + 16);
v137 = 15;
if ( v7 )
{
LABEL_7:
if ( v6 )
{
v8 = *(unsigned __int16 *)(a1 + 6);
v9 = *(unsigned __int16 *)(a1 + 10);
v10 = (*(unsigned __int16 *)(a1 + 4) << 15) + 1109459328;
v11 = (*(unsigned __int16 *)(a1 + 8) << 15) + 1109459328;
v12 = *(unsigned __int16 *)(a1 + 14);
v13 = *(unsigned __int16 *)(a1 + 12) << 15;
*(_DWORD *)(v10 + 4 * v8) = 0;
v14 = v13 + 1109459200;
*(_DWORD *)(v11 + 4 * v9) = a2 & 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
v15 = *(_DWORD *)(v13 + 1109459200 + 4 * v12);
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (a2 >> 1) & 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
v16 = *(_DWORD *)(v13 + 1109459200 + 4 * v12);
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (a2 >> 2) & 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
v17 = v15 != 0;
v18 = v16;
if ( v16 )
v18 = 1;
v19 = *(_DWORD *)(v14 + 4 * v12) != 0;
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (a2 >> 3) & 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
v139 = v19;
v20 = *(_DWORD *)(v14 + 4 * v12);
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (a2 >> 4) & 1;
v21 = v20;
if ( v20 )
v21 = 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
v22 = *(_DWORD *)(v14 + 4 * v12);
v141 = v21;
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (a2 >> 5) & 1;
v23 = v22;
if ( v22 )
v23 = 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
v145 = v23;
v24 = *(_DWORD *)(v14 + 4 * v12);
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (a2 >> 6) & 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
v25 = *(_DWORD *)(v14 + 4 * v12);
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (a2 >> 7) & 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
v26 = v24 != 0;
v27 = v25;
if ( v25 )
v27 = 1;
v28 = v18 | 2 * v17;
v29 = *(_DWORD *)(v14 + 4 * v12);
if ( *(_DWORD *)(v14 + 4 * v12) )
v29 = 1;
result = v29 | 2 * (v27 | 2 * (v26 | 2 * (v145 | 2 * (v141 | 2 * (v139 | 2 * v28)))));
if ( v137 != 7 )
{
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (unsigned __int8)a2 >> 8;
*(_DWORD *)(v10 + 4 * v8) = 1;
result = (*(_DWORD *)(v14 + 4 * v12) != 0) | 2 * result;
if ( v137 > 8 )
{
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (a2 >> 9) & 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
result = (*(_DWORD *)(v14 + 4 * v12) != 0) | 2 * result;
if ( v137 > 9 )
{
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (a2 >> 10) & 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
result = (*(_DWORD *)(v14 + 4 * v12) != 0) | 2 * result;
if ( v137 > 10 )
{
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (a2 >> 11) & 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
result = (*(_DWORD *)(v14 + 4 * v12) != 0) | 2 * result;
if ( v137 > 11 )
{
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (a2 >> 12) & 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
result = (*(_DWORD *)(v14 + 4 * v12) != 0) | 2 * result;
if ( v137 > 12 )
{
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (a2 >> 13) & 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
result = (*(_DWORD *)(v14 + 4 * v12) != 0) | 2 * result;
if ( v137 > 13 )
{
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = (a2 >> 14) & 1;
*(_DWORD *)(v10 + 4 * v8) = 1;
v31 = a2 >> 15;
result = (*(_DWORD *)(v14 + 4 * v12) != 0) | 2 * result;
if ( v137 == 15 )
{
*(_DWORD *)(v10 + 4 * v8) = 0;
*(_DWORD *)(v11 + 4 * v9) = v31;
*(_DWORD *)(v10 + 4 * v8) = 1;
result = (*(_DWORD *)(v14 + 4 * v12) != 0) | 2 * result;
}
}
}
}
}
}
}
}
}
else
{
v82 = *(unsigned __int16 *)(a1 + 6);
v83 = *(unsigned __int16 *)(a1 + 10);
v84 = (*(unsigned __int16 *)(a1 + 4) << 15) + 1109459328;
v85 = (*(unsigned __int16 *)(a1 + 8) << 15) + 1109459328;
v86 = *(unsigned __int16 *)(a1 + 14);
v87 = *(unsigned __int16 *)(a1 + 12) << 15;
*(_DWORD *)(v84 + 4 * v82) = 1;
v88 = v87 + 1109459200;
*(_DWORD *)(v85 + 4 * v83) = a2 & 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
v89 = *(_DWORD *)(v87 + 1109459200 + 4 * v86);
*(_DWORD *)(v84 + 4 * v82) = 1;
*(_DWORD *)(v85 + 4 * v83) = (a2 >> 1) & 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
v90 = *(_DWORD *)(v87 + 1109459200 + 4 * v86);
*(_DWORD *)(v84 + 4 * v82) = 1;
*(_DWORD *)(v85 + 4 * v83) = (a2 >> 2) & 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
v91 = *(_DWORD *)(v87 + 1109459200 + 4 * v86);
*(_DWORD *)(v84 + 4 * v82) = 1;
v92 = v89 != 0;
*(_DWORD *)(v85 + 4 * v83) = (a2 >> 3) & 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
v93 = v90 != 0;
v95 = v91;
v94 = v91 == 0;
v96 = *(_DWORD *)(v88 + 4 * v86);
*(_DWORD *)(v84 + 4 * v82) = 1;
if ( !v94 )
v95 = 1;
*(_DWORD *)(v85 + 4 * v83) = (a2 >> 4) & 1;
v97 = v96;
if ( v96 )
v97 = 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
v98 = *(_DWORD *)(v88 + 4 * v86);
v143 = v97;
*(_DWORD *)(v84 + 4 * v82) = 1;
*(_DWORD *)(v85 + 4 * v83) = (a2 >> 5) & 1;
v99 = v98;
if ( v98 )
v99 = 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
v147 = v99;
v100 = *(_DWORD *)(v88 + 4 * v86);
*(_DWORD *)(v84 + 4 * v82) = 1;
v101 = v100;
if ( v100 )
v101 = 1;
*(_DWORD *)(v85 + 4 * v83) = (a2 >> 6) & 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
v150 = v101;
v102 = *(_DWORD *)(v88 + 4 * v86);
*(_DWORD *)(v84 + 4 * v82) = 1;
*(_DWORD *)(v85 + 4 * v83) = (a2 >> 7) & 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
v140 = v93 | 2 * v92;
v103 = v102 != 0;
v104 = *(_DWORD *)(v88 + 4 * v86);
if ( *(_DWORD *)(v88 + 4 * v86) )
v104 = 1;
result = v104 | 2 * (v103 | 2 * (v150 | 2 * (v147 | 2 * (v143 | 2 * (v95 | 2 * v140)))));
if ( v137 != 7 )
{
*(_DWORD *)(v84 + 4 * v82) = 1;
*(_DWORD *)(v85 + 4 * v83) = (unsigned __int8)a2 >> 8;
*(_DWORD *)(v84 + 4 * v82) = 0;
result = (*(_DWORD *)(v88 + 4 * v86) != 0) | 2 * result;
if ( v137 > 8 )
{
*(_DWORD *)(v84 + 4 * v82) = 1;
*(_DWORD *)(v85 + 4 * v83) = (a2 >> 9) & 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
result = (*(_DWORD *)(v88 + 4 * v86) != 0) | 2 * result;
if ( v137 > 9 )
{
*(_DWORD *)(v84 + 4 * v82) = 1;
*(_DWORD *)(v85 + 4 * v83) = (a2 >> 10) & 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
result = (*(_DWORD *)(v88 + 4 * v86) != 0) | 2 * result;
if ( v137 > 10 )
{
*(_DWORD *)(v84 + 4 * v82) = 1;
*(_DWORD *)(v85 + 4 * v83) = (a2 >> 11) & 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
result = (*(_DWORD *)(v88 + 4 * v86) != 0) | 2 * result;
if ( v137 > 11 )
{
*(_DWORD *)(v84 + 4 * v82) = 1;
*(_DWORD *)(v85 + 4 * v83) = (a2 >> 12) & 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
result = (*(_DWORD *)(v88 + 4 * v86) != 0) | 2 * result;
if ( v137 > 12 )
{
*(_DWORD *)(v84 + 4 * v82) = 1;
*(_DWORD *)(v85 + 4 * v83) = (a2 >> 13) & 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
result = (*(_DWORD *)(v88 + 4 * v86) != 0) | 2 * result;
if ( v137 > 13 )
{
*(_DWORD *)(v84 + 4 * v82) = 1;
*(_DWORD *)(v85 + 4 * v83) = (a2 >> 14) & 1;
*(_DWORD *)(v84 + 4 * v82) = 0;
v105 = a2 >> 15;
result = (*(_DWORD *)(v88 + 4 * v86) != 0) | 2 * result;
if ( v137 == 15 )
{
*(_DWORD *)(v84 + 4 * v82) = 1;
*(_DWORD *)(v85 + 4 * v83) = v105;
*(_DWORD *)(v84 + 4 * v82) = 0;
v106 = *(_DWORD *)(v88 + 4 * v86);
if ( *(_DWORD *)(v88 + 4 * v86) )
v106 = 1;
result = v106 | 2 * result;
}
}
}
}
}
}
}
}
}
goto LABEL_27;
}
LABEL_40:
v40 = *(unsigned __int16 *)(a1 + 12);
v41 = *(unsigned __int16 *)(a1 + 8);
v42 = *(unsigned __int16 *)(a1 + 4);
if ( v6 )
{
v43 = *(unsigned __int16 *)(a1 + 14);
v44 = *(unsigned __int16 *)(a1 + 6);
v45 = *(unsigned __int16 *)(a1 + 10);
v46 = (v42 << 15) + 1109459328;
v47 = (v41 << 15) + 1109459328;
v48 = (v40 << 15) + 1109459200;
v49 = *(_DWORD *)((v40 << 15) + 0x42210100 + 4 * v43);
*(_DWORD *)(v47 + 4 * v45) = a2 & 1;
*(_DWORD *)(v46 + 4 * v44) = v7;
*(_DWORD *)(v46 + 4 * v44) = 1;
v50 = *(_DWORD *)((v40 << 15) + 0x42210100 + 4 * v43);
*(_DWORD *)(v47 + 4 * v45) = (a2 >> 1) & 1;
*(_DWORD *)(v46 + 4 * v44) = v7;
*(_DWORD *)(v46 + 4 * v44) = 1;
v51 = *(_DWORD *)(v48 + 4 * v43);
v52 = v49;
if ( v49 )
v52 = 1;
*(_DWORD *)(v47 + 4 * v45) = (a2 >> 2) & 1;
v53 = v50 != 0;
v54 = v51;
if ( v51 )
v54 = 1;
*(_DWORD *)(v46 + 4 * v44) = v7;
*(_DWORD *)(v46 + 4 * v44) = 1;
v55 = *(_DWORD *)(v48 + 4 * v43);
*(_DWORD *)(v47 + 4 * v45) = (a2 >> 3) & 1;
v142 = v54;
*(_DWORD *)(v46 + 4 * v44) = v7;
v56 = v55;
*(_DWORD *)(v46 + 4 * v44) = 1;
if ( v55 )
v56 = 1;
v57 = *(_DWORD *)(v48 + 4 * v43) != 0;
v146 = v56;
*(_DWORD *)(v47 + 4 * v45) = (a2 >> 4) & 1;
*(_DWORD *)(v46 + 4 * v44) = v7;
*(_DWORD *)(v46 + 4 * v44) = 1;
v58 = *(_DWORD *)(v48 + 4 * v43);
*(_DWORD *)(v47 + 4 * v45) = (a2 >> 5) & 1;
*(_DWORD *)(v46 + 4 * v44) = v7;
*(_DWORD *)(v46 + 4 * v44) = 1;
v149 = v57;
v59 = *(_DWORD *)(v48 + 4 * v43);
*(_DWORD *)(v47 + 4 * v45) = (a2 >> 6) & 1;
*(_DWORD *)(v46 + 4 * v44) = v7;
*(_DWORD *)(v46 + 4 * v44) = 1;
v60 = v53 | 2 * v52;
v61 = v58 != 0;
v62 = v59 != 0;
v63 = *(_DWORD *)(v48 + 4 * v43);
if ( *(_DWORD *)(v48 + 4 * v43) )
v63 = 1;
*(_DWORD *)(v47 + 4 * v45) = (a2 >> 7) & 1;
result = v63 | 2 * (v62 | 2 * (v61 | 2 * (v149 | 2 * (v146 | 2 * (v142 | 2 * v60)))));
*(_DWORD *)(v46 + 4 * v44) = v7;
*(_DWORD *)(v46 + 4 * v44) = 1;
if ( v137 != 7 )
{
v64 = *(_DWORD *)(v48 + 4 * v43) != 0;
*(_DWORD *)(v47 + 4 * v45) = (unsigned __int8)a2 >> 8;
result = v64 | 2 * result;
*(_DWORD *)(v46 + 4 * v44) = v7;
*(_DWORD *)(v46 + 4 * v44) = 1;
if ( v137 > 8 )
{
v65 = *(_DWORD *)(v48 + 4 * v43) != 0;
*(_DWORD *)(v47 + 4 * v45) = (a2 >> 9) & 1;
result = v65 | 2 * result;
*(_DWORD *)(v46 + 4 * v44) = v7;
*(_DWORD *)(v46 + 4 * v44) = 1;
if ( v137 > 9 )
{
v66 = *(_DWORD *)(v48 + 4 * v43) != 0;
*(_DWORD *)(v47 + 4 * v45) = (a2 >> 10) & 1;
result = v66 | 2 * result;
*(_DWORD *)(v46 + 4 * v44) = v7;
*(_DWORD *)(v46 + 4 * v44) = 1;
if ( v137 > 10 )
{
v67 = *(_DWORD *)(v48 + 4 * v43) != 0;
*(_DWORD *)(v47 + 4 * v45) = (a2 >> 11) & 1;
result = v67 | 2 * result;
*(_DWORD *)(v46 + 4 * v44) = v7;
*(_DWORD *)(v46 + 4 * v44) = 1;
if ( v137 > 11 )
{
v68 = *(_DWORD *)(v48 + 4 * v43) != 0;
*(_DWORD *)(v47 + 4 * v45) = (a2 >> 12) & 1;
result = v68 | 2 * result;
*(_DWORD *)(v46 + 4 * v44) = v7;
*(_DWORD *)(v46 + 4 * v44) = 1;
if ( v137 > 12 )
{
v69 = *(_DWORD *)(v48 + 4 * v43) != 0;
*(_DWORD *)(v47 + 4 * v45) = (a2 >> 13) & 1;
result = v69 | 2 * result;
*(_DWORD *)(v46 + 4 * v44) = v7;
*(_DWORD *)(v46 + 4 * v44) = 1;
if ( v137 > 13 )
{
v70 = *(_DWORD *)(v48 + 4 * v43) != 0;
*(_DWORD *)(v47 + 4 * v45) = (a2 >> 14) & 1;
v71 = a2 >> 15;
*(_DWORD *)(v46 + 4 * v44) = v7;
result = v70 | 2 * result;
*(_DWORD *)(v46 + 4 * v44) = 1;
if ( v137 == 15 )
{
v72 = *(_DWORD *)(v48 + 4 * v43) != 0;
*(_DWORD *)(v47 + 4 * v45) = v71;
result = v72 | 2 * result;
*(_DWORD *)(v46 + 4 * v44) = 0;
*(_DWORD *)(v46 + 4 * v44) = 1;
}
}
}
}
}
}
}
}
}
else
{
v107 = *(unsigned __int16 *)(a1 + 14);
v108 = *(unsigned __int16 *)(a1 + 6);
v109 = *(unsigned __int16 *)(a1 + 10);
v110 = (v42 << 15) + 1109459328;
v111 = (v41 << 15) + 1109459328;
v112 = (v40 << 15) + 1109459200;
v113 = *(_DWORD *)((v40 << 15) + 0x42210100 + 4 * v107);
*(_DWORD *)(v111 + 4 * v109) = a2 & 1;
*(_DWORD *)(v110 + 4 * v108) = 1;
*(_DWORD *)(v110 + 4 * v108) = 0;
v114 = *(_DWORD *)((v40 << 15) + 0x42210100 + 4 * v107);
*(_DWORD *)(v111 + 4 * v109) = (a2 >> 1) & 1;
*(_DWORD *)(v110 + 4 * v108) = 1;
*(_DWORD *)(v110 + 4 * v108) = 0;
v115 = *(_DWORD *)(v112 + 4 * v107);
v116 = v113;
if ( v113 )
v116 = 1;
*(_DWORD *)(v111 + 4 * v109) = (a2 >> 2) & 1;
v117 = v114 != 0;
v118 = v115;
if ( v115 )
v118 = 1;
*(_DWORD *)(v110 + 4 * v108) = 1;
*(_DWORD *)(v110 + 4 * v108) = 0;
v119 = *(_DWORD *)(v112 + 4 * v107);
*(_DWORD *)(v111 + 4 * v109) = (a2 >> 3) & 1;
v144 = v118;
*(_DWORD *)(v110 + 4 * v108) = 1;
v120 = v119;
*(_DWORD *)(v110 + 4 * v108) = 0;
if ( v119 )
v120 = 1;
v121 = *(_DWORD *)(v112 + 4 * v107) != 0;
v148 = v120;
*(_DWORD *)(v111 + 4 * v109) = (a2 >> 4) & 1;
*(_DWORD *)(v110 + 4 * v108) = 1;
*(_DWORD *)(v110 + 4 * v108) = 0;
v122 = *(_DWORD *)(v112 + 4 * v107);
*(_DWORD *)(v111 + 4 * v109) = (a2 >> 5) & 1;
*(_DWORD *)(v110 + 4 * v108) = 1;
*(_DWORD *)(v110 + 4 * v108) = 0;
v151 = v121;
v123 = *(_DWORD *)(v112 + 4 * v107);
*(_DWORD *)(v111 + 4 * v109) = (a2 >> 6) & 1;
*(_DWORD *)(v110 + 4 * v108) = 1;
*(_DWORD *)(v110 + 4 * v108) = 0;
v124 = v117 | 2 * v116;
v125 = v122 != 0;
v126 = v123 != 0;
v127 = *(_DWORD *)(v112 + 4 * v107);
if ( *(_DWORD *)(v112 + 4 * v107) )
v127 = 1;
*(_DWORD *)(v111 + 4 * v109) = (a2 >> 7) & 1;
result = v127 | 2 * (v126 | 2 * (v125 | 2 * (v151 | 2 * (v148 | 2 * (v144 | 2 * v124)))));
*(_DWORD *)(v110 + 4 * v108) = 1;
*(_DWORD *)(v110 + 4 * v108) = 0;
if ( v137 != 7 )
{
v128 = *(_DWORD *)(v112 + 4 * v107) != 0;
*(_DWORD *)(v111 + 4 * v109) = (unsigned __int8)a2 >> 8;
result = v128 | 2 * result;
*(_DWORD *)(v110 + 4 * v108) = 1;
*(_DWORD *)(v110 + 4 * v108) = 0;
if ( v137 > 8 )
{
v129 = *(_DWORD *)(v112 + 4 * v107) != 0;
*(_DWORD *)(v111 + 4 * v109) = (a2 >> 9) & 1;
result = v129 | 2 * result;
*(_DWORD *)(v110 + 4 * v108) = 1;
*(_DWORD *)(v110 + 4 * v108) = 0;
if ( v137 > 9 )
{
v130 = *(_DWORD *)(v112 + 4 * v107) != 0;
*(_DWORD *)(v111 + 4 * v109) = (a2 >> 10) & 1;
result = v130 | 2 * result;
*(_DWORD *)(v110 + 4 * v108) = 1;
*(_DWORD *)(v110 + 4 * v108) = 0;
if ( v137 > 10 )
{
v131 = *(_DWORD *)(v112 + 4 * v107) != 0;
*(_DWORD *)(v111 + 4 * v109) = (a2 >> 11) & 1;
result = v131 | 2 * result;
*(_DWORD *)(v110 + 4 * v108) = 1;
*(_DWORD *)(v110 + 4 * v108) = 0;
if ( v137 > 11 )
{
v132 = *(_DWORD *)(v112 + 4 * v107) != 0;
*(_DWORD *)(v111 + 4 * v109) = (a2 >> 12) & 1;
result = v132 | 2 * result;
*(_DWORD *)(v110 + 4 * v108) = 1;
*(_DWORD *)(v110 + 4 * v108) = 0;
if ( v137 > 12 )
{
v133 = *(_DWORD *)(v112 + 4 * v107) != 0;
*(_DWORD *)(v111 + 4 * v109) = (a2 >> 13) & 1;
result = v133 | 2 * result;
*(_DWORD *)(v110 + 4 * v108) = 1;
*(_DWORD *)(v110 + 4 * v108) = 0;
if ( v137 > 13 )
{
v134 = *(_DWORD *)(v112 + 4 * v107) != 0;
*(_DWORD *)(v111 + 4 * v109) = (a2 >> 14) & 1;
v135 = a2 >> 15;
*(_DWORD *)(v110 + 4 * v108) = 1;
result = v134 | 2 * result;
*(_DWORD *)(v110 + 4 * v108) = 0;
if ( v137 == 15 )
{
v136 = *(_DWORD *)(v112 + 4 * v107) != 0;
*(_DWORD *)(v111 + 4 * v109) = v135;
*(_DWORD *)(v110 + 4 * v108) = 1;
result = v136 | 2 * result;
*(_DWORD *)(v110 + 4 * v108) = 0;
}
}
}
}
}
}
}
}
}
LABEL_27:
if ( v138 )
{
v73 = (result >> 7) & 1 | 2
* ((result >> 6) & 1 | 2
* ((result >> 5) & 1 | 2
* ((result >> 4) & 1 | 2
* ((result >> 3) & 1 | 2 * ((result >> 2) & 1 | 2 * (2 * result & 2 | (result >> 1) & 1))))));
v74 = result >> 8;
if ( v137 == 7
|| (v73 = v74 & 1 | 2 * v73, v75 = result >> 9, v137 <= 8)
|| (v73 = v75 & 1 | 2 * v73, v76 = result >> 10, v137 <= 9)
|| (v73 = v76 & 1 | 2 * v73, v77 = result >> 11, v137 <= 10) )
{
result = v73;
}
else
{
v78 = v77 & 1 | 2 * v73;
v79 = result >> 12;
if ( v137 <= 11
|| (v78 = v79 & 1 | 2 * v78, v80 = result >> 13, v137 <= 12)
|| (v78 = v80 & 1 | 2 * v78, v137 <= 13)
|| (v78 = (result >> 14) & 1 | 2 * v78, v81 = result >> 15, v137 != 15) )
{
result = v78;
}
else
{
result = v81 | 2 * v78;
}
}
}
return result;
}其实有些地方它并不是十分准确，因为我是不停地对一个volatile修饰的变量进行读写，而IDA的F5会把这些大量的volatile读写操作整理成一长句，或者搞没。所以不能太信任它。
ARM不同于牙膏厂x86，它没有缓存的概念，也没有乱序执行。而且因为ARM有个三级流水线，每次跳转都要浪费两个周期的时间，所以要尽量减少跳转的次数。
但该做成函数的还是要做成函数，如果啥都内联的话，STM32F103的64K ROM是不够用的。 每个循环单独写成一个函数就好 牺牲点性能没啥大不了的
现在arm被冷落了 大多开始转向risc-v了
https://en.wikipedia.org/wiki/RISC-V
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