TI中文支持网TITLE: Fast cos function for the C28x + Floating-Point Unit.
;
; DESCRIPTION:
;
; This function computes a 32-bit floating point cos given a
; radian input. This function uses the FPU math tables to
; compute the cos.
;
; FUNCTIONS:
;
; float32 cos (float32 radian)
;
; ASSUMPTIONS:
;
; * FPUsinTable and FPUcosTable are linked into the project.
;
; ALGORITHM:
;
; The cos value is calculated as follows:
;
; 1) The offset into a 512 word sin/cos table is calculated:
; k = 0x1FF & (int(Radian*512/(2*pi)))
;
;
; 2) The fractional component between table samples is
; calculated:
; x = fract(Radian*512/2*pi) * (2*pi)/512
;
; 3) The output sine value is calculated as follows:
;
; cos(Radian) = C(k) + x*(-S(k) + x*(-0.5*C(k) + 0.166667*x*S(k)))
;
; sin(Radian) = S(k) + x*(C(k) + x*(-0.5*S(k) – 0.166667*x*C(k)))
;
; where S(k) = Sin table value at offset "k"
; C(k) = Cos table value at offset "k"
; ###########################################################################
; $TI Release: C28x FPU fastRTS Library V1.00 $
; $Release Date: August 6, 2008 $
; ###########################################################################
.page
.global _cos
.ref _FPUsinTable
.ref _FPUcosTable
.text
_cos: ; R0H = Radian (on entry)
MOVIZ R1H,#0x42A2 ; R1H = 512/(2*pi) = 512/6.28318531 = 81.4873309
MOVXI R1H,#0xF983
MPYF32 R0H, R0H, R1H ; R0H = Radian * 512/(2*pi)
MOVIZ R2H,#0x3C49 ; R2H = (2*pi)/512 = 6.28318531/512
MOVXI R2H,#0x0FDB ; = 0x3C490FDB or 0.012271846644531
F32TOI32 R1H, R0H ; R1H = int(Radian * 512/(2*pi))
MOVL XAR6,#_FPUsinTable
MOVL XAR7,#_FPUcosTable
MOV32 ACC, R1H ; ACC = int(Radian *512/(2*pi))
AND @AL,#0x1FF
LSL AL,#1
MOVZ AR0,@AL ; AR0 = Index into "sin/cos" table = k
FRACF32 R0H, R0H ; R0H = fract(Radian*512/(2*pi))
MOVIZ R3H,#0x3E2A ; R3H = 0.166667 (0x3E2AAAAB)
MOVXI R3H,#0xAAAB
MPYF32 R2H, R0H, R2H ; R2H = x = fract(Radian*512/(2*pi)) * (2*pi)/512
//MOV32 R1H,*+XAR6[AR0] ; R1H = S(k)
MPYF32 R3H, R3H, R1H ; R3H = .166*C(k)
//MOV32 R0H,*+XAR7[AR0] ; R0H = C(k)
MPYF32 R0H, -0.5, R0H ; R0H = -.5*C(k)
MPYF32 R3H, R2H, R3H ; R1H = x*0.166667*S(k)
NOP
ADDF32 R0H, R0H, R3H ; R0H = -.5*C(k) + 0.166667*x*S(k)
NOP
MPYF32 R3H, R2H, R0H ; R3H = x*(-.5*C(k) + 0.166667*x*S(k))
//MOV32 R1H, *+XAR6[AR0] ; R1H = S(k)
NOP
SUBF32 R3H, R3H, R1H ; R3H = -S(k) + x*(-.5*C(k) + 0.166667*x*S(k))
NOP
MPYF32 R3H, R2H, R3H ; R3H = x*(-S(k) + x*(-.5*C(k) + 0.166667*x*S(k)))
//MOV32 R0H, *+XAR7[AR0] ; R0H = C(k)
NOP
ADDF32 R0H, R0H, R3H ; R0H = cos(Radian) = C(k) + x*(-S(k) + x*(-.5*C(k) + 0.166667*x*S(k)))
LRETR
.endasmfunc
CMD文件中数学表也已经添加进去了
FPUTABLES : origin = 0x3FD860, length = 0x0006A0 /* FPU Tables in Boot ROM */
FPUmathTables : > FPUTABLES, PAGE = 0, TYPE = NOLOAD
我现在计算出来的cos值出错，
cos_in = 0.0;
cos_out = cos(cos_in);
cos_out 计算出来不等于1，
如果TI的算法没错，我怀疑是_FPUsinTable 和_FPUcosTable 里的值有问题。有人遇到同样的问题吗
