diff options
Diffstat (limited to 'libc/i386fp/fpullf.x')
| -rw-r--r-- | libc/i386fp/fpullf.x | 101 |
1 files changed, 101 insertions, 0 deletions
diff --git a/libc/i386fp/fpullf.x b/libc/i386fp/fpullf.x new file mode 100644 index 0000000..417ef92 --- /dev/null +++ b/libc/i386fp/fpullf.x @@ -0,0 +1,101 @@ +! bcc 386 floating point routines (version 2) -- Fpullf +! authors: Timothy Murphy (tim@maths.tcd.ie), Bruce Evans + +#include "fplib.h" + + .extern fpoverflow + .extern fpunderflow + +! pop double from stack, convert to float and store at address [ebx] + + .globl Fpullf + .align ALIGNMENT +Fpullf: + +! Step 1: load and shift left + + mov eax,PC_SIZE+D_LOW[esp] ! lower dword + mov edx,PC_SIZE+D_HIGH[esp] ! upper dword + mov ecx,edx ! copy upper dword into ecx ... + and ecx,#D_SIGN_MASK ! ... and extract sign + and edx,#D_EXP_MASK | D_FRAC_MASK ! extract exponent and fraction + sub edx,#(D_EXP_BIAS-F_EXP_BIAS) << D_EXP_SHIFT ! adjust exponent bias + jz underflow + cmp edx,#F_EXP_INFINITE << D_EXP_SHIFT ! check if exponent lies in reduced range + jae outofbounds + shld edx,eax,#D_EXP_BIT-F_EXP_BIT ! shift exponent and fraction + +! Step 2: round + + test eax,#1 << (REG_BIT-1-(D_EXP_BIT-F_EXP_BIT)) ! test upper rounding bit + jz step3 ! below middle, don't round up + test eax,#(1 << (REG_BIT-1-(D_EXP_BIT-F_EXP_BIT)))-1 ! test other rounding bits + jnz roundup ! above middle, round up + test dl,#1 ! in middle, check parity bit + jz step3 ! already even, otherwise round up to make even + +roundup: + inc edx ! carry 1 + test edx,#F_FRAC_MASK ! is fraction now 0? (carry into F_EXPMASK) + jnz step3 ! no -- carry complete + cmp edx,#(F_EXP_INFINITE << F_EXP_SHIFT) & ~F_NORM_MASK ! yes (very unlikely): check for overflow + ! XXX - I think these tests say 0x7e7fffff overflows + jae overflow + +! Step 3: put it all together + +step3: + or edx,ecx ! include sign + mov F_HIGH[ebx],edx ! store the result in [ebx] + ret #D_SIZE ! return and release double from stack + + .align ALIGNMENT +outofbounds: + jns overflow ! have just compared exponent with the max +underflow: +! call fpunderflow ! XXX + push ecx ! save sign + mov ecx,edx + and ecx,#~D_FRAC_MASK ! assume fraction is below exp + cmp ecx,#-((D_EXP_BIAS-F_EXP_BIAS) << D_EXP_SHIFT) ! was exp = 0? + jz exp_x_0 + shr ecx,#D_EXP_SHIFT + neg ecx + and edx,#D_FRAC_MASK + or edx,#D_NORM_MASK + shld edx,eax,#D_EXP_BIT-F_EXP_BIT-1 + shl eax,#D_EXP_BIT-F_EXP_BIT-1 + push ebx ! save to use for rounding + sub ebx,ebx + shrd ebx,eax,cl + shrd eax,edx,cl + shr edx,cl + cmp eax,#1 << (REG_BIT-1) + jb over_denorm_roundup + ja denorm_roundup + test dl,#1 + jz over_denorm_roundup +denorm_roundup: +#if F_NORM_BIT != F_EXP_SHIFT +#include "carry into norm bit doesn't go into low exp bit" +#endif + inc edx +over_denorm_roundup: + pop ebx + pop ecx + or edx,ecx + mov F_HIGH[ebx],edx + ret #D_SIZE + + .align ALIGNMENT +exp_x_0: ! XXX check for denormals - they underflow + pop ecx + mov dword F_HIGH[ebx],#0 + ret #D_SIZE + + .align ALIGNMENT +overflow: + mov edx,ebx ! put sign in usual reg + call fpoverflow + mov F_HIGH[ebx],dword #F_HUGE_HIGH ! XXX - should use infinity + ret #D_SIZE ! ... if fpoverflow does |