1. 数学模型对于一个目的像素，其坐标通过反向变换得到的在原图中的浮点坐标为(i+u,j+v)，其中 i、j均为非负整数，u、v为［0,1)区间的浮点数，双三次插值考虑一个浮点坐标(i+u,j+v)周围 的16个邻点，目的像素值f(i+u,j+v)可由如下插值公式得到：f(i+u,j+v) = [A]* [B] * [C][A]=[ S(u + 1) S(u + 0)S(u - 1) S(u - 2)]厂[B]= II Lf(i-1, j-1) f(i+0, j-1) f(i+1, j-1) f(i+2, j-1)f(i-1, j+0)f(i+0, j+0)f(i+1, j+0)f(i+2, j+0)f(i-1, j+1)f(i+0, j+1)f(i+1, j+1)f(i+2, j+1)f(i-1, j+2)f(i+0, j+2)f(i+1, j+2)f(i+2, j+2)nIIJ厂[C]= II LS(v + 1) nS(v + 0)S(v - 1)S(v - 2),0<=Abs(x)<1,1<=Abs(x)<2,Abs(x)>=2 n )，为插值核厂 1-2*Abs(x)A2+Abs(x)A3S(x)= { 4-8*Abs(x)+5*Abs(x)A2-Abs(x)A3L 0S(x)是对Sin(x*Pi)/x的逼近(Pi是圆周率2. 计算流程1. 获取16个点的坐标P1、P2……P162. 由插值核计算公式S(x)分别计算出x、y方向的插值核向量Su、Sv3. 进行矩阵运算，得到插值结果iTemp1 = Su0 * P1 + Su1 * P5 + Su2 * P9 + Su3 * P13iTemp2 = Su0 * P2 + Su1 * P6 + Su2 * P10 + Su3 * P14iTemp3 = Su0 * P3 + Su1 * P7 + Su2 * P11 + Su3 * P15iTemp4 = Su0 * P4 + Su1 * P8 + Su2 * P12 + Su3 * P16iResult = Sv1 * iTemp1 + Sv2 * iTemp2 + Sv3 * iTemp3 + Sv4 * iTemp44. 在得到插值结果图后，我们发现图像中有“毛刺”，因此对插值结果做了个后处理， 即：设该点在原图中的像素值为pSrc，若abs(iResult - pSrc)大于某阈值，我们认为插值后 的点可能污染原图，因此用原像素值pSrc代替。
3. 算法优化由于双三次插值计算一个点的坐标需要其周围16个点，更有多达20次的乘法及15次 的加法，计算量可以说是非常大，势必要进行优化我们选择了 Intel的SSE2优化技术，它只支持在P4及以上的机器测试当前CPU是 否支持SSE2，可由CPUID指令得到，代码为：BOOL g_bSSE2 = FALSE;—asm{mov eax, 1;cpuid;test edx, 0x04000000;jz NotSupport;mov g_bSSE2, 1NotSupport:}支持SSE2的CPU引入了 8个128位的寄存器，这样一个寄存器中就可以存放4个点 （RGB），有利于并行计算详细代码见 Transform.cpp 中函数 Optimize_Bicubic优化中遇到的问题：1. 图像每个点由RGB通道组成，由于1个SSE2寄存器有16个字节，这样读入4个像 素点后，要浪费4个字节，同时要花费时间将数据对齐，即由BRGB | RGBR | GBRG | BRGB 对齐成 0RGB | 0RGB | 0RGB | 0RGB ;2. 读16字节数据到寄存器时，由于图像地址不能保证是16字节对齐，因此需用更多 时钟周期的MOVDQU指令（6个以上时钟周期）；如能使地址16字节对齐，则可用MOVDQA 指令（1个时钟周期）;3. 为了消除除法及浮点运算，对权值放大256倍，这样在计算插值核时，必须用2Bytes 来表示1个系数，而图像数据都是1Byte，这样在对齐做乘法时，要浪费一半的SSE2寄存 器的空间，导致运算时间变长；而若降低插值核的精度，使其在1Byte表示范围内时，运算 的精度又大为下降；4. 对各指令的周期以及若干行指令是否能够并行流水缺乏经验和认识。
附：SSE2指令整理算术（Arithmetic）指令:ADDPD--Packed Double-Precision Floating-Point Add SSE22个double对应相加ADDPD xmm0, xmm1/m128ADDPS--Packed Single-Precision Floating-Point Add SSE4个float对应相加ADDPS xmm0, xmm1/m128ADDSD--Scalar Double-Precision Floating-Point Add 1个double（低端）对应相加 SSE2ADDSD xmm0, xmm1/m64ADDSS--Scalar Single-Precision Floating-Point Add SSE1个float（低端）对应相加ADDSS xmm0, xmm1/m32PADDB/PADDW/PADDD--Packed AddOpcodeInstructionDescription0F FC /rPADDB mm, mm/m64Add packed byte integers from mm/m64 and mm.66 0F FC /rPADDBxmm1,xmm2/m128Add packed byte integers from xmm2/m128 and xmm1.0F FD /rPADDW mm, mm/m64Add packed word integers from mm/m64 and mm.66 0F FD /rPADDW xmm1,xmm2/m128Add packed word integers from xmm2/m128 and xmm1.0F FE /rPADDD mm, mm/m64Add packed doubleword integers from mm/m64 and mm.66 0F FE /rPADDD xmm1,xmm2/m128Add packed doubleword integers from xmm2/m128 and xmm1.PADDQ--Packed Quadword AddOpcodeInstructionDescription0F D4 /rPADDQ mm1,mm2/m64Add quadword integer mm2/m64 to mm166 0F D4 /rPADDQxmm1,xmm2/m128Add packed quadword integers xmm2/m128 to xmm1PADDSB/PADDSW--Packed Add with SaturationOpcodeInstructionDescription0F EC /rPADDSB mm,mm/m64Add packed signed byte integers from mm/m64 and mm and saturate the results.66 0F EC /rPADDSB xmm1, xmm2/m128Add packed signed byte integers from xmm2/m128 and xmm1 saturate the results.0F ED /rPADDSW mm,mm/m64Add packed signed word integers from mm/m64 and mm and saturate the results.66 0F ED /rPADDSW xmm1, xmm2/m128Add packed signed word integers from xmm2/m128 and xmm1 and saturate the results.PADDUSB/PADDUSW--Packed Add Unsigned with SaturationOpcodeInstructionDescription0F DC /rPADDUSB mm,mm/m64Add packed unsigned byte integers from mm/m64 and mm and saturate the results.66 0F DC /rPADDUSB xmm1, xmm2/m128Add packed unsigned byte integers from xmm2/m128 and xmm1 saturate the results.0F DD /rPADDUSW mm,mm/m64Add packed unsigned word integers from mm/m64 and mm and saturate the results.66 0FDD /rPADDUSW xmm1, xmm2/m128Add packed unsigned word integers from xmm2/m128 to xmm1 and saturate the results.PMADDWD--Packed Multiply and AddOpcodeInstructionDescription0F F5 /rPMADDWD mm, mm/m64Multiply the packed words in mm by the packed words in mm/m64. Add the 32-bit pairs of results and store in mm as doubleword66 0FF5 /rPMADDWD xmml, xmm2/m128Multiply the packed word integers in xmml by the packed word integers in xmm2/m128, and add the adjacent doubleword results.PSADBW--Packed Sum of Absolute DifferencesOpcodeInstructionDescription0F F6 /rPSADBW mm1, mm2/m64Absolute difference of packed unsigned byte integers from mm2 /m64 and mm1; differences are then summed to produce an unsigned word integer result.66 0FF6 /rPSADBW xmm1, xmm2/m128Absolute difference of packed unsigned byte integers from xmm2 /m128 and xmm1; the 8 low differences and 8 high differences are then summed separately to produce two word integer results.SRCX?X6X5X4XJX2X1xoDESTY?Y6Y5Y4YJY2Y1TEMPABS(X7-YT|AB9：X6-Yff|AB9：X1-Y1iAB^XO-YOjDESTOOHOOHOOHOOHOOHOOHSUM：TRdP7...THdP0|PSUBB/PSUBW/PSUBD--Packed SubtractOpcodeInstructionDescription0F F8 /rPSUBB mm,mm/m64Subtract packed byte integers in mm/m64 from packed byte integers in mm.66 0F F8 /rPSUBB xmm1, xmm2/m128Subtract packed byte integers in xmm2/m128 from packed byte integers in xmm1.0F F9 /rPSUBW mm,Subtract packed word integers in mm/m64 frommm/m64packed word integers in mm.66 0F F9 /rPSUBW xmml, xmm2/m128Subtract packed word integers in xmm2/m128 from packed word integers in xmm1.0F FA /rPSUBD mm,mm/m64Subtract packed doubleword integers in mm/m64 from packed doubleword integers in mm.66 0F FA /rPSUBD xmml, xmm2/m128Subtract packed doubleword integers in xmm2/mem128 from packed doubleword integers in xmm1.PSUBQ--Packed Subtract QuadwordOpcodeInstructionDescription0F FB /rPSUBQ mm2/m64mm1,Subtract quadword integer in mm1 from mm2 /m64.66 0F FB /rPSUBQ xmm2/m128xmm1,Subtract packed quadword integers in xmm1 from xmm2 /m128.PSUBSB/PSUBSW--Packed Subtract with SaturationOpcodeInstructionDescription0F E8 /rPSUBSB mm,mm/m64Subtract signed packed bytes in mm/m64 from signed packed bytes in mm and saturate results.66 0F E8 /rPSUBSB xmm1, xmm2/m128Subtract packed signed byte integers in xmm2/m128 from packed signed byte integers in xmm1 and saturate results.0F E9 /rPSUBSW mm, mm/m64Subtract signed packed words in mm/m64 from signed packed words in mm and saturate results.66 0F E9 /rPSUBSW xmm1, xmm2/m128Subtract packed signed word integers in xmm2/m128 from packed signed word integers in xmm1 and saturate results.PSUBUSB/PSUBUSW--Packed Subtract Unsigned with SaturationOpcodeInstructionDescription0F D8 /rPSUBUSB mm, mm/m64Subtract unsigned packed bytes in mm/m64 from unsigned packed bytes in mm and saturate result.66 0FPSUBUSB xmm1,Subtract packed unsigned byte integers inD8 /rxmm2/m128xmm2/m128 from packed unsigned byte integers in xmml and saturate result.0F D9 /rPSUBUSW mm, mm/m64Subtract unsigned packed words in mm/m64 from unsigned packed words in mm and saturate result.66 0FD9 /rPSUBUSW xmml, xmm2/m128Subtract packed unsigned word integers in xmm2/m128 from packed unsigned word integers in xmm1 and saturate result.SUBPD--Packed Double-Precision Floating-Point SubtractOpcodeInstructionDescription66 0F 5C /rSUBPD xmm1,xmm2/m128Subtract packed double-precision floating-point values in xmm2/m128 from xmm1.SUBPS--Packed Single-Precision Floating-Point SubtractOpcodeInstructionDescription0F 5C /rSUBPS xmm1xmm2/m128Subtract packed single-precision floating-point values in xmm2/mem from xmm1.SUBSD--Scalar Double-Precision Floating-Point SubtractOpcodeInstructionDescriptionF2 0F 5C /rSUBSD xmm1, xmm2/m64Subtracts the low double-precision floating-point numbers in xmm2/mem64 from xmm1.SUBSS--Scalar Single-FP SubtractOpcodeInstructionDescription砰5CSUBSS xmm1, xmm2/m32Subtract the lower single-precision floating-point numbers in xmm2/m32 from xmm1.PMULHUW--Packed Multiply High UnsignedOpcodeInstructionDescription0F E4 /rPMULHUW mm1,Multiply the packed unsigned word integers in mm1mm2/m64register and mm2/m64, and store the high 16 bits of the results in mm1.66 0FE4 /rPMULHUW xmml, xmm2/m128Multiply the packed unsigned word integers in xmm1 and xmm2/m128, and store the high 16 bits of the results in xmm1.SRCXJX2X1xoDESTYJY2Y1YOZJ = XJ i YJZ2 =X2 Y2zi = xi i riZO = XO YODEGTZ3(31-I6]Z2(3l -16]Zl[3l-I6]zq31-16]TEMPPMULHW--Packed Multiply High SignedOpcodeInstructionDescription0F E5 /rPMULHW mm, mm/m64Multiply the packed signed word integers in mm1 register and mm2/m64, and store the high 16 bits of the results in mm1.66 0FE5 /rPMULHW xmm1, xmm2/m128Multiply the packed signed word integers in xmm1 and xmm2/m128, and store the high 16 bits of the results in xmm1.PMULLW--Packed Multiply Low SignedOpcodeInstructionDescription0F D5 /rPMULLW mm, mm/m64Multiply the packed signed word integers in mm1 register and mm2/m64, and store the low 16 bits of the results in mm1.66 0FD5 /rPMULLW xmm1, xmm2/m128Multiply the packed signed word integers in xmm1 and xmm2/m128, and store the low 16 bits of the results in xmm1.PMULUDQ--Multiply Doubleword UnsignedOpcodeInstructionDescription0F F4 /rPMULUDQ mm1,Multiply unsigned doubleword integer in mm1 bymm2/m64unsigned doubleword integer in mm2/m64, and store the quadword result in mm1.66 OFF4 /rPMULUDQ xmm1, xmm2/m128Multiply packed unsigned doubleword integers in xmm1 by packed unsigned doubleword integers in xmm2/m128, and store the quadword results in xmm1.PMULUDQ instruction with 64-Bit operands:DEST[63-0] ~DEST[31-0] * SRC[31-0];PMULUDQ instruction with 128-Bit operands:DEST[63-0] —DEST[31-0] * SRC[31-0];DEST[127-64] ~DEST[95-64] * SRC[95-64];MULPD--Packed Double-Precision Floating-Point MultiplyOpcodeInstructionDescription66 0F 59 /rMULPD xmm1,xmm2/m128Multiply packed double-precision floating-point values in xmm2/m128 by xmm1.DEST[63-0] ~DEST[63-0] * SRC[63-0];DEST[127-64] —DEST[127-64] * SRC[127-64];MULPS--Packed Single-Precision Floating-Point MultiplyOpcodeInstructionDescription0F 59 /rMULPS xmm1,xmm2/m128Multiply packed single-precision floating-point values in xmm2/mem by xmm1.DEST[31-0] ~DEST[31-0] * SRC[31-0];DEST[63-32] ~DEST[63-32] * SRC[63-32];DEST[95-64] —DEST[95-64] * SRC[95-64];DEST[127-96] -DEST[127-96] * SRC[127-96];MULSD--Scalar Double-Precision Floating-Point MultiplyOpcodeInstructionDescriptionF2 0F59 /rMULSD xmm1, xmm2/m64Multiply the low double-precision floating-point value in xmm2/mem64 by low double-precision floating-point value in xmm1.DEST[63-0] ~DEST[63-0] * xmm2/m64[63-0];* DEST[127-64] remains unchanged *;MULSS--Scalar Single-FP MultiplyOpcodeInstructionDescriptionF3 0F 59 /rMULSS xmm1, xmm2/m32Multiply the low single-precision floating-point value in xmm2/mem by the low single-precision floating-point value in xmm1.DEST[31-0] ~DEST[31-0] * SRC[31-0];* DEST[127-32] remains unchanged *;DIVPD--Packed Double-Precision Floating-Point DivideDIVPD xmm0, xmm1/m128DEST[63-0] ~DEST[63-0] / (SRC[63-0]);DEST[127-64] —DEST[127-64] / (SRC[127-64]);DIVPS--Packed Single-Precision Floating-Point DivideDIVPS xmm0, xmm1/m128DEST[31-0] ~DEST[31-0] / (SRC[31-0]);DEST[63-32] ~DEST[63-32] / (SRC[63-32]);DEST[95-64] —DEST[95-64] / (SRC[95-64]);DEST[127-96] ~DEST[127-96] / (SRC[127-96]);DIVSD--Scalar Double-Precision Floating-Point DivideDIVSD xmm0, xmm1/m64DEST[63-0] ~DEST[63-0] / SRC[63-0];* DEST[127-64] remains unchanged *;DIVSS--Scalar Single-Precision Floating-Point DivideDIVSS xmm0, xmm1/m32DEST[31-0] ~DEST[31-0] / SRC[31-0];* DEST[127-32] remains unchanged *;PAVGB/PAVGW--Packed AverageOpcodeInstructionDescription0F E0 /rPAVGB mm1,mm2/m64Average packed unsigned byte integers from mm2/m64 and mm1, with rounding.66 0F E0, /rPAVGB xmm2/m128xmml,Average packed unsigned byte integers from xmm2/m128 and xmm1, with rounding.0F E3 /rPAVGW mm2/m64mml,Average packed unsigned word integers from mm2/m64 and mm1, with rounding.66 0F E3 /rPAVGW xmm2/m128xmml,Average packed unsigned word integers from xmm2/m128 and xmm1, with rounding.PMAXSW--Packed Signed Integer Word MaximumOpcodeInstructionDescription0F EE /rPMAXSW mm1,mm2/m64Compare signed word integers in mm2/m64 and mm1 for maximum values.66 0F EE /rPMAXSW xmm1, xmm2/m128Compare signed word integers in xmm2/m128 and xmm1 for maximum values.PMAXUB--Packed Unsigned Integer Byte MaximumOpcodeInstructionDescription0F DE /rPMAXUB mm1,mm2/m64Compare unsigned byte integers in mm2/m64 and mm1 for maximum values.66 0F DE /rPMAXUB xmm1,xmm2/m128Compare unsigned byte integers in xmm2/m128 and xmm1 for maximum values.PMINSW--Packed Signed Integer Word MinimumOpcodeInstructionDescription0F EA /rPMINSW mm1,mm2/m64Compare signed word integers in mm2/m64 and mm1 for minimum values.66 0F EA /rPMINSW xmm1,xmm2/m128Compare signed word integers in xmm2/m128 and xmm1 for minimum values.PMINUB--Packed Unsigned Integer Byte MinimumOpcodeInstructionDescription0F DA /rPMINUB mm2/m64mm1,Compare unsigned byte integers in mm2/m64 and mm1 for minimum values.66 0F DA /rPMINUB xmm2/m128xmml, Compare unsigned byte integers in xmm2/m128 and xmm1 for minimum values.RCPPS--Packed Single-Precision Floating-Point ReciprocalOpcodeInstructionDescription0F 53 /rRCPPS xmm1, xmm2/m128Returns to xmm1 the packed approximations of the reciprocals of the packed single-precision floating-point values in xmm2/m128.DEST[31-0] JAPPROXIMATE(1.0/(SRC[31-0]));DEST[63-32] ~APPROXIMATE(1.0/(SRC[63-32]));DEST[95-64] ~APPROXIMATE(1.0/(SRC[95-64]));DEST[127-96] ~APPROXIMATE(1.0/(SRC[127-96]));RCPSS--Scalar Single-Precision Floating-Point ReciprocalOpcodeInstructionDescriptionF3 0F 53 /rRCPSS xmm1, xmm2/m32Returns to xmm1 the packed approximation of the reciprocal of the low single-precision floating-point value in xmm2/m32.DEST[31-0] -APPROX (1.0/(SRC[31-0]));* DEST[127-32] remains unchanged *;RSQRTPS--Packed Single-Precision Floating-Point Square Root ReciprocalOpcodeInstructionDescription0F 52 /rRSQRTPS xmm1, xmm2/m128Returns to xmm1 the packed approximations of the reciprocals of the square roots of the packed single-precision floating-point values in xmm2/m128.DEST[31-0] ~APPROXIMATE(1.0/SQRT(SRC[31-0]));DEST[63-32] ~APPROXIMATE(1.0/SQRT(SRC[63-32]));DEST[95-64] ~APPROXIMATE(1.0/SQRT(SRC[95-64]));DEST[127-96] JAPPROXIMATE(1.0/SQRT(SRC[127-96]));RSQRTSS--Scalar Single-Precision Floating-Point Square Root ReciprocalOpcodeInstructionDescriptionF3 0FRSQRTSSReturns to xmm1 an approximation of the reciprocal of52 /rxmml, xmm2/m32the square root of the low single-precision floating-point value in xmm2/m32.DEST[31-0] ~APPROXIMATE(1.0/SQRT(SRC[31-0]));* DEST[127-32] remains unchanged *;SQRTPD--Packed Double-Precision Floating-Point Square RootOpcodeInstructionDescription66 0F 51 /rSQRTPD xmm1, xmm2/m128Computes square roots of the packed double-precision floating-point values in xmm2/m128 and stores the results in xmm1.SQRTPS--Packed Single-Precision Floating-Point Square RootOpcodeInstructionDescription0F 51 /rSQRTPS xmm1, xmm2/m128Computes square roots of the packed single-precision floating-point values in xmm2/m128 and stores the results in xmm1.SQRTSD--Scalar Double-Precision Floating-Point Square RootOpcodeInstructionDescriptionF2 0F 51 /rSQRTSD xmm1, xmm2/m64Computes square root of the low double-precision floating-point value in xmm2/m64 and stores the results in xmm1.SQRTSS--Scalar Single-Precision Floating-Point Square RootOpcodeInstructionDescriptionF3 0F 51 /rSQRTSS xmm1, xmm2/m32Computes square root of the low single-precision floating-point value in xmm2/m32 and stores the results in xmm1.移动(Move)指令:MASKMOVDQU--Mask Move of Double Quadword UnalignedMASKMOVDQU xmm0, xmm1MASKMOVQ--Mask Move of QuadwordMASKMOVQ mm0, mm1MOVAPD--Move Aligned Packed Double-Precision Floating-Point ValuesMOVAPD xmm0, xmm1/m128MOVAPD xmm1/m128, xmm0MOVAPS--Move Aligned Packed Single-Precision Floating-Point ValuesMOVAPS xmm0, xmm1/m128MOVD--Move DoublewordInstructionDescriptionMOVD mm, r/m32Move doubleword from r/m32 to mm.MOVD r/m32, mmMove doubleword from mm to r/m32.MOVD xmm, r/m32Move doubleword from r/m32 to xmm.MOVD r/m32, xmmMove doubleword from xmm register to r/m32.MOVDQ2Q - Move QuadwordInstructionDescriptionMOVDQ2Q mm, xmmMove low quadword from xmm to mmx register .MOVQ2DQ--Move QuadwordOpcodeInstructionDescriptionF3 0FMOVQ2DQ xmm,Move quadword from mmx to low quadword ofD6mmxmm.DEST[63-0] ~SRC[63-0];DEST[127-64] —00000000000000000H;MOVDQA - Move Aligned Double QuadwordInstructionDescriptionMOVDQAxmm1,Move aligned double quadword from xmm2/m128 toxmm2/m128xmm1.0MOVDQA xmm1xmm2/m128,Move aligned double quadword from xmm1 to xmm2/m128.MOVDQU - Move Unaligned Double QuadwordInstructionDescriptionMOVDQUxmm1,Move unaligned double quadword from xmm2/m128xmm2/m128to xmm1.MOVDQUxmm2/m128,Move unaligned double quadword from xmm1 toxmm1xmm2/m128.MOVHLPS-- Move Packed Single-Precision Floating-Point Values High to LowInstructionDescriptionMOVHLPS xmm1, xmm2Move two packed single-precision floating-point values from high quadword of xmm2 to low quadword of xmm1.DEST[63-0] —SRC[127-64];* DEST[127-64] unchanged *;MOVLHPS - Move Packed Single-Precision Floating-Point Values Low to HighInstructionDescriptionMOVLHPS xmm1, xmm2Move two packed single-precision floating-point values from low quadword of xmm2 to high quadword of xmm1.MOVHPD--Move High Packed Double-Precision Floating-Point ValueInstructionDescriptionMOVHPD xmm, m64Move double-precision floating-point value from m64 to high quadword of xmm.MOVHPD m64,xmmMove double-precision floating-point value from high quadword of xmm to m64.MOVHPD instruction for memory to XMM move:DEST[127-64] —SRC ;* DEST[63-0] unchanged *;MOVHPD instruction for XMM to memory move: DEST —SRC[127-64];MOVHPS--Move High Packed Single-Precision Floating-Point ValuesInstructionDescriptionMOVHPS xmm, m64Move two packed single-precision floating-point values from m64 to high quadword of xmm.MOVHPS m64, xmmMove two packed single-precision floating-point values from high quadword of xmm to m64.MOVLPD--Move Low Packed Double-Precision Floating-Point ValueInstructionDescriptionMOVLPD xmm, m64Move double-precision floating-point value from m64 to low quadword of xmm register.MOVLPD m64, xmmMove double-precision floating-point nvalue from low quadword of xmm register to m64.MOVLPS - Move Low Packed Single-Precision Floating-Point ValuesOpcodeInstructionDescription0F 12MOVLPS xmm,Move two packed single-precision floating-point values/rm64from m64 to low quadword of xmm.0F 13MOVLPS m64,Move two packed single-precision floating-point values/rxmmfrom low quadword o。