第42部分-Linux x86 64位彙編SSE指令

SSE架構提供對打包單精度浮點值的SIMD支援。資料傳送到XMM寄存器中。

SSE指令有兩個版本，字尾PS和字尾SS。PS是對打包單精度浮點值執行類型的運算操作，每個值都參與。SS結尾的，隻對打包值中的低位雙字執行。

傳送資料

傳送單精度浮點值很大程度上依賴于值是否在記憶體中對準了。

MOVAPS指令要求資料在記憶體中對準16位元組邊界。如果不對準會出現分段錯誤。

gas彙編器使用.align指令來把資料對準特定的記憶體邊界。

處理資料

運算指令如下；

這些指令都是用兩個操作數，源操作數可以是128位記憶體或者XMM寄存器，目标操作數必須是XMM寄存器。

sse示例

.section .data
.align 16
value1:
   .float 12.34, 2345., -93.2, 10.44
value2:
   .float 39.234, 21.4, 100.94, 10.56
.section .bss
   .lcomm result, 16
.section .text
.globl _start
_start:
   nop
   movaps value1, %xmm0
   movaps value2, %xmm1

   addps %xmm1, %xmm0
   sqrtps %xmm0, %xmm0
   maxps %xmm1, %xmm0
   movaps %xmm0, result

   movl $60, %eax
   movl $0, %ebx
   syscall
           

把單精度浮點值加載到XMM寄存器中。并執行基本運算操作，XMM0結果被傳送回記憶體中使用标簽result标記的位置中。

as -g -o ssemath.o ssemath.s

ld -o ssemath ssemath.o

使用gdb進行過程中的檢視:

(gdb) print $xmm0

$3 = {v4_float = {12.3400002, 2345, -93.1999969, 10.4399996}, v2_double = {5.6101725574714474e+24, 754974.88032836909}, v16_int8 = {-92, 112, 69, 65, 0, -112, 18, 69, 102, 102, -70,

    -62, 61, 10, 39, 65}, v8_int16 = {28836, 16709, -28672, 17682, 26214, -15686, 2621, 16679}, v4_int32 = {1095069860, 1158844416, -1027971482, 1093077565}, v2_int64 = {

    4977198868967288996, 4694732396933310054}, uint128 = 86602527020781775578804592404012036260}

(gdb) print $xmm1

$4 = {v4_float = {39.2340012, 21.3999996, 100.940002, 10.5600004}, v2_double = {228170145.05651563, 817889.63044647221}, v16_int8 = {-98, -17, 28, 66, 51, 51, -85, 65, 72, -31, -55,

    66, -61, -11, 40, 65}, v8_int16 = {-4194, 16924, 13107, 16811, -7864, 17097, -2621, 16680}, v4_int32 = {1109192606, 1101738803, 1120526664, 1093203395}, v2_int64 = {

    4731932128728379294, 4695272830521696584}, uint128 = 86612496260875578387995842694967259038}

相加addps後：

(gdb) s

18     sqrtps %xmm0, %xmm0

(gdb) print $xmm0

$5 = {v4_float = {51.5740013, 2366.3999, 7.74000549, 21}, v2_double = {6.014405302368266e+24, 201326624.48375034}, v16_int8 = {-57, 75, 78, 66, 102, -26, 19, 69, 32, -82, -9, 64, 0,

    0, -88, 65}, v8_int16 = {19399, 16974, -6554, 17683, -20960, 16631, 0, 16808}, v4_int32 = {1112427463, 1158932070, 1089973792, 1101529088}, v2_int64 = {4977575340048010183,

    4731031409642679840}, uint128 = 87272125618359850373392885123090631623}

sqrtps後,求平方：

(gdb) s

19     maxps %xmm1, %xmm0

(gdb) print $xmm0

$6 = {v4_float = {7.18150425, 48.6456566, 2.78208661, 4.5825758}, v2_double = {159623578059.61627, 1193.1154792614809}, v16_int8 = {-30, -50, -27, 64, 39, -107, 66, 66, -75, 13, 50,

    64, 118, -92, -110, 64}, v8_int16 = {-12574, 16613, -27353, 16962, 3509, 16434, -23434, 16530}, v4_int32 = {1088802530, 1111659815, 1077022133, 1083352182}, v2_int64 = {

    4774542550791212770, 4652962192817262005}, uint128 = 85832002755546427910696780764134362850}

maxps後,計算兩個打包值中最大值:

(gdb) s

20     movaps %xmm0, result

(gdb) print $xmm0

$7 = {v4_float = {39.2340012, 48.6456566, 100.940002, 10.5600004}, v2_double = {159623578681.87201, 817889.63044647221}, v16_int8 = {-98, -17, 28, 66, 39, -107, 66, 66, 72, -31,

    -55, 66, -61, -11, 40, 65}, v8_int16 = {-4194, 16924, -27353, 16962, -7864, 17097, -2621, 16680}, v4_int32 = {1109192606, 1111659815, 1120526664, 1093203395}, v2_int64 = {

    4774542550811602846, 4695272830521696584}, uint128 = 86612496260875578388038453117050482590}

movaps後，result得到結果:

(gdb) x /4f &result

0x600100 <result>: 39.2340012  48.6456566  100.940002  10.5600004

比較指令

SSE的比較指令同MMX比較指令類似，單獨比較128位打包單精度浮點值的每個元素。

其中CMPSS有3個操作數

CMPPS imp, source,destination

imp可以有如下：

結果是位掩碼，存放在寄存器XMM0中。

Gas彙編器提供了替代imp操作數的僞指令，如下：

比較示例

.section .data
.align 16
value1:
   .float 12.34, 2345., -93.2, 10.44
value2:
   .float 12.34, 21.4, -93.2, 10.45
.section .bss
   .lcomm result, 16
.section .text
.globl _start
_start:
   nop
   movaps value1, %xmm0
   movaps value2, %xmm1

   cmpeqps %xmm1, %xmm0
   movaps %xmm0, result

   movl $60, %eax
   movl $0, %ebx
   syscall
           

as -g -o ssecomp.o ssecomp.s

ld -o ssecomp ssecomp.o

比較前：

(gdb) print $xmm0

$1 = {v4_float = {12.3400002, 2345, -93.1999969, 10.4399996}, v2_double = {5.6101725574714474e+24, 754974.88032836909}, v16_int8 = {-92, 112, 69, 65, 0, -112, 18, 69, 102, 102, -70,

    -62, 61, 10, 39, 65}, v8_int16 = {28836, 16709, -28672, 17682, 26214, -15686, 2621, 16679}, v4_int32 = {1095069860, 1158844416, -1027971482, 1093077565}, v2_int64 = {

    4977198868967288996, 4694732396933310054}, uint128 = 86602527020781775578804592404012036260}

(gdb) print $xmm1

$2 = {v4_float = {12.3400002, 21.3999996, -93.1999969, 10.4499998}, v2_double = {228170144.635625, 760217.88032836909}, v16_int8 = {-92, 112, 69, 65, 51, 51, -85, 65, 102, 102, -70,

    -62, 51, 51, 39, 65}, v8_int16 = {28836, 16709, 13107, 16811, 26214, -15686, 13107, 16679}, v4_int32 = {1095069860, 1101738803, -1027971482, 1093088051}, v2_int64 = {

    4731932128714256548, 4694777433960375910}, uint128 = 86603357807293900154403331565622227108}

比較後:

(gdb) print $xmm0

$3 = {v4_float = {-nan(0x7fffff), 0, -nan(0x7fffff), 0}, v2_double = {2.1219957904712067e-314, 2.1219957904712067e-314}, v16_int8 = {-1, -1, -1, -1, 0, 0, 0, 0, -1, -1, -1, -1, 0,

    0, 0, 0}, v8_int16 = {-1, -1, 0, 0, -1, -1, 0, 0}, v4_int32 = {-1, 0, -1, 0}, v2_int64 = {4294967295, 4294967295}, uint128 = 79228162495817593524129366015}

 (gdb) x /4x &result

0x600100 <result>: 0xffffffff  0x00000000  0xffffffff  0x00000000

表示第一個和第三個整數相等。

sse整數指令

sse提供處理64位打包整數值的一些擴充特性。擴充了MMX提供的功能。如下：