summaryrefslogtreecommitdiff
path: root/arch/i386/math-emu/reg_round.S
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /arch/i386/math-emu/reg_round.S
downloadconfigs-2.6.12-rc2.tar.gz
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'arch/i386/math-emu/reg_round.S')
-rw-r--r--arch/i386/math-emu/reg_round.S708
1 files changed, 708 insertions, 0 deletions
diff --git a/arch/i386/math-emu/reg_round.S b/arch/i386/math-emu/reg_round.S
new file mode 100644
index 00000000000..d1d4e48b4f6
--- /dev/null
+++ b/arch/i386/math-emu/reg_round.S
@@ -0,0 +1,708 @@
+ .file "reg_round.S"
+/*---------------------------------------------------------------------------+
+ | reg_round.S |
+ | |
+ | Rounding/truncation/etc for FPU basic arithmetic functions. |
+ | |
+ | Copyright (C) 1993,1995,1997 |
+ | W. Metzenthen, 22 Parker St, Ormond, Vic 3163, |
+ | Australia. E-mail billm@suburbia.net |
+ | |
+ | This code has four possible entry points. |
+ | The following must be entered by a jmp instruction: |
+ | fpu_reg_round, fpu_reg_round_sqrt, and fpu_Arith_exit. |
+ | |
+ | The FPU_round entry point is intended to be used by C code. |
+ | From C, call as: |
+ | int FPU_round(FPU_REG *arg, unsigned int extent, unsigned int control_w) |
+ | |
+ | Return value is the tag of the answer, or-ed with FPU_Exception if |
+ | one was raised, or -1 on internal error. |
+ | |
+ | For correct "up" and "down" rounding, the argument must have the correct |
+ | sign. |
+ | |
+ +---------------------------------------------------------------------------*/
+
+/*---------------------------------------------------------------------------+
+ | Four entry points. |
+ | |
+ | Needed by both the fpu_reg_round and fpu_reg_round_sqrt entry points: |
+ | %eax:%ebx 64 bit significand |
+ | %edx 32 bit extension of the significand |
+ | %edi pointer to an FPU_REG for the result to be stored |
+ | stack calling function must have set up a C stack frame and |
+ | pushed %esi, %edi, and %ebx |
+ | |
+ | Needed just for the fpu_reg_round_sqrt entry point: |
+ | %cx A control word in the same format as the FPU control word. |
+ | Otherwise, PARAM4 must give such a value. |
+ | |
+ | |
+ | The significand and its extension are assumed to be exact in the |
+ | following sense: |
+ | If the significand by itself is the exact result then the significand |
+ | extension (%edx) must contain 0, otherwise the significand extension |
+ | must be non-zero. |
+ | If the significand extension is non-zero then the significand is |
+ | smaller than the magnitude of the correct exact result by an amount |
+ | greater than zero and less than one ls bit of the significand. |
+ | The significand extension is only required to have three possible |
+ | non-zero values: |
+ | less than 0x80000000 <=> the significand is less than 1/2 an ls |
+ | bit smaller than the magnitude of the |
+ | true exact result. |
+ | exactly 0x80000000 <=> the significand is exactly 1/2 an ls bit |
+ | smaller than the magnitude of the true |
+ | exact result. |
+ | greater than 0x80000000 <=> the significand is more than 1/2 an ls |
+ | bit smaller than the magnitude of the |
+ | true exact result. |
+ | |
+ +---------------------------------------------------------------------------*/
+
+/*---------------------------------------------------------------------------+
+ | The code in this module has become quite complex, but it should handle |
+ | all of the FPU flags which are set at this stage of the basic arithmetic |
+ | computations. |
+ | There are a few rare cases where the results are not set identically to |
+ | a real FPU. These require a bit more thought because at this stage the |
+ | results of the code here appear to be more consistent... |
+ | This may be changed in a future version. |
+ +---------------------------------------------------------------------------*/
+
+
+#include "fpu_emu.h"
+#include "exception.h"
+#include "control_w.h"
+
+/* Flags for FPU_bits_lost */
+#define LOST_DOWN $1
+#define LOST_UP $2
+
+/* Flags for FPU_denormal */
+#define DENORMAL $1
+#define UNMASKED_UNDERFLOW $2
+
+
+#ifndef NON_REENTRANT_FPU
+/* Make the code re-entrant by putting
+ local storage on the stack: */
+#define FPU_bits_lost (%esp)
+#define FPU_denormal 1(%esp)
+
+#else
+/* Not re-entrant, so we can gain speed by putting
+ local storage in a static area: */
+.data
+ .align 4,0
+FPU_bits_lost:
+ .byte 0
+FPU_denormal:
+ .byte 0
+#endif /* NON_REENTRANT_FPU */
+
+
+.text
+.globl fpu_reg_round
+.globl fpu_Arith_exit
+
+/* Entry point when called from C */
+ENTRY(FPU_round)
+ pushl %ebp
+ movl %esp,%ebp
+ pushl %esi
+ pushl %edi
+ pushl %ebx
+
+ movl PARAM1,%edi
+ movl SIGH(%edi),%eax
+ movl SIGL(%edi),%ebx
+ movl PARAM2,%edx
+
+fpu_reg_round: /* Normal entry point */
+ movl PARAM4,%ecx
+
+#ifndef NON_REENTRANT_FPU
+ pushl %ebx /* adjust the stack pointer */
+#endif /* NON_REENTRANT_FPU */
+
+#ifdef PARANOID
+/* Cannot use this here yet */
+/* orl %eax,%eax */
+/* jns L_entry_bugged */
+#endif /* PARANOID */
+
+ cmpw EXP_UNDER,EXP(%edi)
+ jle L_Make_denorm /* The number is a de-normal */
+
+ movb $0,FPU_denormal /* 0 -> not a de-normal */
+
+Denorm_done:
+ movb $0,FPU_bits_lost /* No bits yet lost in rounding */
+
+ movl %ecx,%esi
+ andl CW_PC,%ecx
+ cmpl PR_64_BITS,%ecx
+ je LRound_To_64
+
+ cmpl PR_53_BITS,%ecx
+ je LRound_To_53
+
+ cmpl PR_24_BITS,%ecx
+ je LRound_To_24
+
+#ifdef PECULIAR_486
+/* With the precision control bits set to 01 "(reserved)", a real 80486
+ behaves as if the precision control bits were set to 11 "64 bits" */
+ cmpl PR_RESERVED_BITS,%ecx
+ je LRound_To_64
+#ifdef PARANOID
+ jmp L_bugged_denorm_486
+#endif /* PARANOID */
+#else
+#ifdef PARANOID
+ jmp L_bugged_denorm /* There is no bug, just a bad control word */
+#endif /* PARANOID */
+#endif /* PECULIAR_486 */
+
+
+/* Round etc to 24 bit precision */
+LRound_To_24:
+ movl %esi,%ecx
+ andl CW_RC,%ecx
+ cmpl RC_RND,%ecx
+ je LRound_nearest_24
+
+ cmpl RC_CHOP,%ecx
+ je LCheck_truncate_24
+
+ cmpl RC_UP,%ecx /* Towards +infinity */
+ je LUp_24
+
+ cmpl RC_DOWN,%ecx /* Towards -infinity */
+ je LDown_24
+
+#ifdef PARANOID
+ jmp L_bugged_round24
+#endif /* PARANOID */
+
+LUp_24:
+ cmpb SIGN_POS,PARAM5
+ jne LCheck_truncate_24 /* If negative then up==truncate */
+
+ jmp LCheck_24_round_up
+
+LDown_24:
+ cmpb SIGN_POS,PARAM5
+ je LCheck_truncate_24 /* If positive then down==truncate */
+
+LCheck_24_round_up:
+ movl %eax,%ecx
+ andl $0x000000ff,%ecx
+ orl %ebx,%ecx
+ orl %edx,%ecx
+ jnz LDo_24_round_up
+ jmp L_Re_normalise
+
+LRound_nearest_24:
+ /* Do rounding of the 24th bit if needed (nearest or even) */
+ movl %eax,%ecx
+ andl $0x000000ff,%ecx
+ cmpl $0x00000080,%ecx
+ jc LCheck_truncate_24 /* less than half, no increment needed */
+
+ jne LGreater_Half_24 /* greater than half, increment needed */
+
+ /* Possibly half, we need to check the ls bits */
+ orl %ebx,%ebx
+ jnz LGreater_Half_24 /* greater than half, increment needed */
+
+ orl %edx,%edx
+ jnz LGreater_Half_24 /* greater than half, increment needed */
+
+ /* Exactly half, increment only if 24th bit is 1 (round to even) */
+ testl $0x00000100,%eax
+ jz LDo_truncate_24
+
+LGreater_Half_24: /* Rounding: increment at the 24th bit */
+LDo_24_round_up:
+ andl $0xffffff00,%eax /* Truncate to 24 bits */
+ xorl %ebx,%ebx
+ movb LOST_UP,FPU_bits_lost
+ addl $0x00000100,%eax
+ jmp LCheck_Round_Overflow
+
+LCheck_truncate_24:
+ movl %eax,%ecx
+ andl $0x000000ff,%ecx
+ orl %ebx,%ecx
+ orl %edx,%ecx
+ jz L_Re_normalise /* No truncation needed */
+
+LDo_truncate_24:
+ andl $0xffffff00,%eax /* Truncate to 24 bits */
+ xorl %ebx,%ebx
+ movb LOST_DOWN,FPU_bits_lost
+ jmp L_Re_normalise
+
+
+/* Round etc to 53 bit precision */
+LRound_To_53:
+ movl %esi,%ecx
+ andl CW_RC,%ecx
+ cmpl RC_RND,%ecx
+ je LRound_nearest_53
+
+ cmpl RC_CHOP,%ecx
+ je LCheck_truncate_53
+
+ cmpl RC_UP,%ecx /* Towards +infinity */
+ je LUp_53
+
+ cmpl RC_DOWN,%ecx /* Towards -infinity */
+ je LDown_53
+
+#ifdef PARANOID
+ jmp L_bugged_round53
+#endif /* PARANOID */
+
+LUp_53:
+ cmpb SIGN_POS,PARAM5
+ jne LCheck_truncate_53 /* If negative then up==truncate */
+
+ jmp LCheck_53_round_up
+
+LDown_53:
+ cmpb SIGN_POS,PARAM5
+ je LCheck_truncate_53 /* If positive then down==truncate */
+
+LCheck_53_round_up:
+ movl %ebx,%ecx
+ andl $0x000007ff,%ecx
+ orl %edx,%ecx
+ jnz LDo_53_round_up
+ jmp L_Re_normalise
+
+LRound_nearest_53:
+ /* Do rounding of the 53rd bit if needed (nearest or even) */
+ movl %ebx,%ecx
+ andl $0x000007ff,%ecx
+ cmpl $0x00000400,%ecx
+ jc LCheck_truncate_53 /* less than half, no increment needed */
+
+ jnz LGreater_Half_53 /* greater than half, increment needed */
+
+ /* Possibly half, we need to check the ls bits */
+ orl %edx,%edx
+ jnz LGreater_Half_53 /* greater than half, increment needed */
+
+ /* Exactly half, increment only if 53rd bit is 1 (round to even) */
+ testl $0x00000800,%ebx
+ jz LTruncate_53
+
+LGreater_Half_53: /* Rounding: increment at the 53rd bit */
+LDo_53_round_up:
+ movb LOST_UP,FPU_bits_lost
+ andl $0xfffff800,%ebx /* Truncate to 53 bits */
+ addl $0x00000800,%ebx
+ adcl $0,%eax
+ jmp LCheck_Round_Overflow
+
+LCheck_truncate_53:
+ movl %ebx,%ecx
+ andl $0x000007ff,%ecx
+ orl %edx,%ecx
+ jz L_Re_normalise
+
+LTruncate_53:
+ movb LOST_DOWN,FPU_bits_lost
+ andl $0xfffff800,%ebx /* Truncate to 53 bits */
+ jmp L_Re_normalise
+
+
+/* Round etc to 64 bit precision */
+LRound_To_64:
+ movl %esi,%ecx
+ andl CW_RC,%ecx
+ cmpl RC_RND,%ecx
+ je LRound_nearest_64
+
+ cmpl RC_CHOP,%ecx
+ je LCheck_truncate_64
+
+ cmpl RC_UP,%ecx /* Towards +infinity */
+ je LUp_64
+
+ cmpl RC_DOWN,%ecx /* Towards -infinity */
+ je LDown_64
+
+#ifdef PARANOID
+ jmp L_bugged_round64
+#endif /* PARANOID */
+
+LUp_64:
+ cmpb SIGN_POS,PARAM5
+ jne LCheck_truncate_64 /* If negative then up==truncate */
+
+ orl %edx,%edx
+ jnz LDo_64_round_up
+ jmp L_Re_normalise
+
+LDown_64:
+ cmpb SIGN_POS,PARAM5
+ je LCheck_truncate_64 /* If positive then down==truncate */
+
+ orl %edx,%edx
+ jnz LDo_64_round_up
+ jmp L_Re_normalise
+
+LRound_nearest_64:
+ cmpl $0x80000000,%edx
+ jc LCheck_truncate_64
+
+ jne LDo_64_round_up
+
+ /* Now test for round-to-even */
+ testb $1,%bl
+ jz LCheck_truncate_64
+
+LDo_64_round_up:
+ movb LOST_UP,FPU_bits_lost
+ addl $1,%ebx
+ adcl $0,%eax
+
+LCheck_Round_Overflow:
+ jnc L_Re_normalise
+
+ /* Overflow, adjust the result (significand to 1.0) */
+ rcrl $1,%eax
+ rcrl $1,%ebx
+ incw EXP(%edi)
+ jmp L_Re_normalise
+
+LCheck_truncate_64:
+ orl %edx,%edx
+ jz L_Re_normalise
+
+LTruncate_64:
+ movb LOST_DOWN,FPU_bits_lost
+
+L_Re_normalise:
+ testb $0xff,FPU_denormal
+ jnz Normalise_result
+
+L_Normalised:
+ movl TAG_Valid,%edx
+
+L_deNormalised:
+ cmpb LOST_UP,FPU_bits_lost
+ je L_precision_lost_up
+
+ cmpb LOST_DOWN,FPU_bits_lost
+ je L_precision_lost_down
+
+L_no_precision_loss:
+ /* store the result */
+
+L_Store_significand:
+ movl %eax,SIGH(%edi)
+ movl %ebx,SIGL(%edi)
+
+ cmpw EXP_OVER,EXP(%edi)
+ jge L_overflow
+
+ movl %edx,%eax
+
+ /* Convert the exponent to 80x87 form. */
+ addw EXTENDED_Ebias,EXP(%edi)
+ andw $0x7fff,EXP(%edi)
+
+fpu_reg_round_signed_special_exit:
+
+ cmpb SIGN_POS,PARAM5
+ je fpu_reg_round_special_exit
+
+ orw $0x8000,EXP(%edi) /* Negative sign for the result. */
+
+fpu_reg_round_special_exit:
+
+#ifndef NON_REENTRANT_FPU
+ popl %ebx /* adjust the stack pointer */
+#endif /* NON_REENTRANT_FPU */
+
+fpu_Arith_exit:
+ popl %ebx
+ popl %edi
+ popl %esi
+ leave
+ ret
+
+
+/*
+ * Set the FPU status flags to represent precision loss due to
+ * round-up.
+ */
+L_precision_lost_up:
+ push %edx
+ push %eax
+ call set_precision_flag_up
+ popl %eax
+ popl %edx
+ jmp L_no_precision_loss
+
+/*
+ * Set the FPU status flags to represent precision loss due to
+ * truncation.
+ */
+L_precision_lost_down:
+ push %edx
+ push %eax
+ call set_precision_flag_down
+ popl %eax
+ popl %edx
+ jmp L_no_precision_loss
+
+
+/*
+ * The number is a denormal (which might get rounded up to a normal)
+ * Shift the number right the required number of bits, which will
+ * have to be undone later...
+ */
+L_Make_denorm:
+ /* The action to be taken depends upon whether the underflow
+ exception is masked */
+ testb CW_Underflow,%cl /* Underflow mask. */
+ jz Unmasked_underflow /* Do not make a denormal. */
+
+ movb DENORMAL,FPU_denormal
+
+ pushl %ecx /* Save */
+ movw EXP_UNDER+1,%cx
+ subw EXP(%edi),%cx
+
+ cmpw $64,%cx /* shrd only works for 0..31 bits */
+ jnc Denorm_shift_more_than_63
+
+ cmpw $32,%cx /* shrd only works for 0..31 bits */
+ jnc Denorm_shift_more_than_32
+
+/*
+ * We got here without jumps by assuming that the most common requirement
+ * is for a small de-normalising shift.
+ * Shift by [1..31] bits
+ */
+ addw %cx,EXP(%edi)
+ orl %edx,%edx /* extension */
+ setne %ch /* Save whether %edx is non-zero */
+ xorl %edx,%edx
+ shrd %cl,%ebx,%edx
+ shrd %cl,%eax,%ebx
+ shr %cl,%eax
+ orb %ch,%dl
+ popl %ecx
+ jmp Denorm_done
+
+/* Shift by [32..63] bits */
+Denorm_shift_more_than_32:
+ addw %cx,EXP(%edi)
+ subb $32,%cl
+ orl %edx,%edx
+ setne %ch
+ orb %ch,%bl
+ xorl %edx,%edx
+ shrd %cl,%ebx,%edx
+ shrd %cl,%eax,%ebx
+ shr %cl,%eax
+ orl %edx,%edx /* test these 32 bits */
+ setne %cl
+ orb %ch,%bl
+ orb %cl,%bl
+ movl %ebx,%edx
+ movl %eax,%ebx
+ xorl %eax,%eax
+ popl %ecx
+ jmp Denorm_done
+
+/* Shift by [64..) bits */
+Denorm_shift_more_than_63:
+ cmpw $64,%cx
+ jne Denorm_shift_more_than_64
+
+/* Exactly 64 bit shift */
+ addw %cx,EXP(%edi)
+ xorl %ecx,%ecx
+ orl %edx,%edx
+ setne %cl
+ orl %ebx,%ebx
+ setne %ch
+ orb %ch,%cl
+ orb %cl,%al
+ movl %eax,%edx
+ xorl %eax,%eax
+ xorl %ebx,%ebx
+ popl %ecx
+ jmp Denorm_done
+
+Denorm_shift_more_than_64:
+ movw EXP_UNDER+1,EXP(%edi)
+/* This is easy, %eax must be non-zero, so.. */
+ movl $1,%edx
+ xorl %eax,%eax
+ xorl %ebx,%ebx
+ popl %ecx
+ jmp Denorm_done
+
+
+Unmasked_underflow:
+ movb UNMASKED_UNDERFLOW,FPU_denormal
+ jmp Denorm_done
+
+
+/* Undo the de-normalisation. */
+Normalise_result:
+ cmpb UNMASKED_UNDERFLOW,FPU_denormal
+ je Signal_underflow
+
+/* The number must be a denormal if we got here. */
+#ifdef PARANOID
+ /* But check it... just in case. */
+ cmpw EXP_UNDER+1,EXP(%edi)
+ jne L_norm_bugged
+#endif /* PARANOID */
+
+#ifdef PECULIAR_486
+ /*
+ * This implements a special feature of 80486 behaviour.
+ * Underflow will be signalled even if the number is
+ * not a denormal after rounding.
+ * This difference occurs only for masked underflow, and not
+ * in the unmasked case.
+ * Actual 80486 behaviour differs from this in some circumstances.
+ */
+ orl %eax,%eax /* ms bits */
+ js LPseudoDenormal /* Will be masked underflow */
+#else
+ orl %eax,%eax /* ms bits */
+ js L_Normalised /* No longer a denormal */
+#endif /* PECULIAR_486 */
+
+ jnz LDenormal_adj_exponent
+
+ orl %ebx,%ebx
+ jz L_underflow_to_zero /* The contents are zero */
+
+LDenormal_adj_exponent:
+ decw EXP(%edi)
+
+LPseudoDenormal:
+ testb $0xff,FPU_bits_lost /* bits lost == underflow */
+ movl TAG_Special,%edx
+ jz L_deNormalised
+
+ /* There must be a masked underflow */
+ push %eax
+ pushl EX_Underflow
+ call EXCEPTION
+ popl %eax
+ popl %eax
+ movl TAG_Special,%edx
+ jmp L_deNormalised
+
+
+/*
+ * The operations resulted in a number too small to represent.
+ * Masked response.
+ */
+L_underflow_to_zero:
+ push %eax
+ call set_precision_flag_down
+ popl %eax
+
+ push %eax
+ pushl EX_Underflow
+ call EXCEPTION
+ popl %eax
+ popl %eax
+
+/* Reduce the exponent to EXP_UNDER */
+ movw EXP_UNDER,EXP(%edi)
+ movl TAG_Zero,%edx
+ jmp L_Store_significand
+
+
+/* The operations resulted in a number too large to represent. */
+L_overflow:
+ addw EXTENDED_Ebias,EXP(%edi) /* Set for unmasked response. */
+ push %edi
+ call arith_overflow
+ pop %edi
+ jmp fpu_reg_round_signed_special_exit
+
+
+Signal_underflow:
+ /* The number may have been changed to a non-denormal */
+ /* by the rounding operations. */
+ cmpw EXP_UNDER,EXP(%edi)
+ jle Do_unmasked_underflow
+
+ jmp L_Normalised
+
+Do_unmasked_underflow:
+ /* Increase the exponent by the magic number */
+ addw $(3*(1<<13)),EXP(%edi)
+ push %eax
+ pushl EX_Underflow
+ call EXCEPTION
+ popl %eax
+ popl %eax
+ jmp L_Normalised
+
+
+#ifdef PARANOID
+#ifdef PECULIAR_486
+L_bugged_denorm_486:
+ pushl EX_INTERNAL|0x236
+ call EXCEPTION
+ popl %ebx
+ jmp L_exception_exit
+#else
+L_bugged_denorm:
+ pushl EX_INTERNAL|0x230
+ call EXCEPTION
+ popl %ebx
+ jmp L_exception_exit
+#endif /* PECULIAR_486 */
+
+L_bugged_round24:
+ pushl EX_INTERNAL|0x231
+ call EXCEPTION
+ popl %ebx
+ jmp L_exception_exit
+
+L_bugged_round53:
+ pushl EX_INTERNAL|0x232
+ call EXCEPTION
+ popl %ebx
+ jmp L_exception_exit
+
+L_bugged_round64:
+ pushl EX_INTERNAL|0x233
+ call EXCEPTION
+ popl %ebx
+ jmp L_exception_exit
+
+L_norm_bugged:
+ pushl EX_INTERNAL|0x234
+ call EXCEPTION
+ popl %ebx
+ jmp L_exception_exit
+
+L_entry_bugged:
+ pushl EX_INTERNAL|0x235
+ call EXCEPTION
+ popl %ebx
+L_exception_exit:
+ mov $-1,%eax
+ jmp fpu_reg_round_special_exit
+#endif /* PARANOID */