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Diffstat (limited to 'arch/parisc/math-emu/sfsub.c')
| -rw-r--r-- | arch/parisc/math-emu/sfsub.c | 508 |
1 files changed, 508 insertions, 0 deletions
diff --git a/arch/parisc/math-emu/sfsub.c b/arch/parisc/math-emu/sfsub.c new file mode 100644 index 000000000..583d3ace4 --- /dev/null +++ b/arch/parisc/math-emu/sfsub.c @@ -0,0 +1,508 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Linux/PA-RISC Project (http://www.parisc-linux.org/) + * + * Floating-point emulation code + * Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org> + */ +/* + * BEGIN_DESC + * + * File: + * @(#) pa/spmath/sfsub.c $Revision: 1.1 $ + * + * Purpose: + * Single_subtract: subtract two single precision values. + * + * External Interfaces: + * sgl_fsub(leftptr, rightptr, dstptr, status) + * + * Internal Interfaces: + * + * Theory: + * <<please update with a overview of the operation of this file>> + * + * END_DESC +*/ + + +#include "float.h" +#include "sgl_float.h" + +/* + * Single_subtract: subtract two single precision values. + */ +int +sgl_fsub( + sgl_floating_point *leftptr, + sgl_floating_point *rightptr, + sgl_floating_point *dstptr, + unsigned int *status) + { + register unsigned int left, right, result, extent; + register unsigned int signless_upper_left, signless_upper_right, save; + + register int result_exponent, right_exponent, diff_exponent; + register int sign_save, jumpsize; + register boolean inexact = FALSE, underflowtrap; + + /* Create local copies of the numbers */ + left = *leftptr; + right = *rightptr; + + /* A zero "save" helps discover equal operands (for later), * + * and is used in swapping operands (if needed). */ + Sgl_xortointp1(left,right,/*to*/save); + + /* + * check first operand for NaN's or infinity + */ + if ((result_exponent = Sgl_exponent(left)) == SGL_INFINITY_EXPONENT) + { + if (Sgl_iszero_mantissa(left)) + { + if (Sgl_isnotnan(right)) + { + if (Sgl_isinfinity(right) && save==0) + { + /* + * invalid since operands are same signed infinity's + */ + if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION); + Set_invalidflag(); + Sgl_makequietnan(result); + *dstptr = result; + return(NOEXCEPTION); + } + /* + * return infinity + */ + *dstptr = left; + return(NOEXCEPTION); + } + } + else + { + /* + * is NaN; signaling or quiet? + */ + if (Sgl_isone_signaling(left)) + { + /* trap if INVALIDTRAP enabled */ + if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION); + /* make NaN quiet */ + Set_invalidflag(); + Sgl_set_quiet(left); + } + /* + * is second operand a signaling NaN? + */ + else if (Sgl_is_signalingnan(right)) + { + /* trap if INVALIDTRAP enabled */ + if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION); + /* make NaN quiet */ + Set_invalidflag(); + Sgl_set_quiet(right); + *dstptr = right; + return(NOEXCEPTION); + } + /* + * return quiet NaN + */ + *dstptr = left; + return(NOEXCEPTION); + } + } /* End left NaN or Infinity processing */ + /* + * check second operand for NaN's or infinity + */ + if (Sgl_isinfinity_exponent(right)) + { + if (Sgl_iszero_mantissa(right)) + { + /* return infinity */ + Sgl_invert_sign(right); + *dstptr = right; + return(NOEXCEPTION); + } + /* + * is NaN; signaling or quiet? + */ + if (Sgl_isone_signaling(right)) + { + /* trap if INVALIDTRAP enabled */ + if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION); + /* make NaN quiet */ + Set_invalidflag(); + Sgl_set_quiet(right); + } + /* + * return quiet NaN + */ + *dstptr = right; + return(NOEXCEPTION); + } /* End right NaN or Infinity processing */ + + /* Invariant: Must be dealing with finite numbers */ + + /* Compare operands by removing the sign */ + Sgl_copytoint_exponentmantissa(left,signless_upper_left); + Sgl_copytoint_exponentmantissa(right,signless_upper_right); + + /* sign difference selects sub or add operation. */ + if(Sgl_ismagnitudeless(signless_upper_left,signless_upper_right)) + { + /* Set the left operand to the larger one by XOR swap * + * First finish the first word using "save" */ + Sgl_xorfromintp1(save,right,/*to*/right); + Sgl_xorfromintp1(save,left,/*to*/left); + result_exponent = Sgl_exponent(left); + Sgl_invert_sign(left); + } + /* Invariant: left is not smaller than right. */ + + if((right_exponent = Sgl_exponent(right)) == 0) + { + /* Denormalized operands. First look for zeroes */ + if(Sgl_iszero_mantissa(right)) + { + /* right is zero */ + if(Sgl_iszero_exponentmantissa(left)) + { + /* Both operands are zeros */ + Sgl_invert_sign(right); + if(Is_rounding_mode(ROUNDMINUS)) + { + Sgl_or_signs(left,/*with*/right); + } + else + { + Sgl_and_signs(left,/*with*/right); + } + } + else + { + /* Left is not a zero and must be the result. Trapped + * underflows are signaled if left is denormalized. Result + * is always exact. */ + if( (result_exponent == 0) && Is_underflowtrap_enabled() ) + { + /* need to normalize results mantissa */ + sign_save = Sgl_signextendedsign(left); + Sgl_leftshiftby1(left); + Sgl_normalize(left,result_exponent); + Sgl_set_sign(left,/*using*/sign_save); + Sgl_setwrapped_exponent(left,result_exponent,unfl); + *dstptr = left; + /* inexact = FALSE */ + return(UNDERFLOWEXCEPTION); + } + } + *dstptr = left; + return(NOEXCEPTION); + } + + /* Neither are zeroes */ + Sgl_clear_sign(right); /* Exponent is already cleared */ + if(result_exponent == 0 ) + { + /* Both operands are denormalized. The result must be exact + * and is simply calculated. A sum could become normalized and a + * difference could cancel to a true zero. */ + if( (/*signed*/int) save >= 0 ) + { + Sgl_subtract(left,/*minus*/right,/*into*/result); + if(Sgl_iszero_mantissa(result)) + { + if(Is_rounding_mode(ROUNDMINUS)) + { + Sgl_setone_sign(result); + } + else + { + Sgl_setzero_sign(result); + } + *dstptr = result; + return(NOEXCEPTION); + } + } + else + { + Sgl_addition(left,right,/*into*/result); + if(Sgl_isone_hidden(result)) + { + *dstptr = result; + return(NOEXCEPTION); + } + } + if(Is_underflowtrap_enabled()) + { + /* need to normalize result */ + sign_save = Sgl_signextendedsign(result); + Sgl_leftshiftby1(result); + Sgl_normalize(result,result_exponent); + Sgl_set_sign(result,/*using*/sign_save); + Sgl_setwrapped_exponent(result,result_exponent,unfl); + *dstptr = result; + /* inexact = FALSE */ + return(UNDERFLOWEXCEPTION); + } + *dstptr = result; + return(NOEXCEPTION); + } + right_exponent = 1; /* Set exponent to reflect different bias + * with denomalized numbers. */ + } + else + { + Sgl_clear_signexponent_set_hidden(right); + } + Sgl_clear_exponent_set_hidden(left); + diff_exponent = result_exponent - right_exponent; + + /* + * Special case alignment of operands that would force alignment + * beyond the extent of the extension. A further optimization + * could special case this but only reduces the path length for this + * infrequent case. + */ + if(diff_exponent > SGL_THRESHOLD) + { + diff_exponent = SGL_THRESHOLD; + } + + /* Align right operand by shifting to right */ + Sgl_right_align(/*operand*/right,/*shifted by*/diff_exponent, + /*and lower to*/extent); + + /* Treat sum and difference of the operands separately. */ + if( (/*signed*/int) save >= 0 ) + { + /* + * Difference of the two operands. Their can be no overflow. A + * borrow can occur out of the hidden bit and force a post + * normalization phase. + */ + Sgl_subtract_withextension(left,/*minus*/right,/*with*/extent,/*into*/result); + if(Sgl_iszero_hidden(result)) + { + /* Handle normalization */ + /* A straightforward algorithm would now shift the result + * and extension left until the hidden bit becomes one. Not + * all of the extension bits need participate in the shift. + * Only the two most significant bits (round and guard) are + * needed. If only a single shift is needed then the guard + * bit becomes a significant low order bit and the extension + * must participate in the rounding. If more than a single + * shift is needed, then all bits to the right of the guard + * bit are zeros, and the guard bit may or may not be zero. */ + sign_save = Sgl_signextendedsign(result); + Sgl_leftshiftby1_withextent(result,extent,result); + + /* Need to check for a zero result. The sign and exponent + * fields have already been zeroed. The more efficient test + * of the full object can be used. + */ + if(Sgl_iszero(result)) + /* Must have been "x-x" or "x+(-x)". */ + { + if(Is_rounding_mode(ROUNDMINUS)) Sgl_setone_sign(result); + *dstptr = result; + return(NOEXCEPTION); + } + result_exponent--; + /* Look to see if normalization is finished. */ + if(Sgl_isone_hidden(result)) + { + if(result_exponent==0) + { + /* Denormalized, exponent should be zero. Left operand * + * was normalized, so extent (guard, round) was zero */ + goto underflow; + } + else + { + /* No further normalization is needed. */ + Sgl_set_sign(result,/*using*/sign_save); + Ext_leftshiftby1(extent); + goto round; + } + } + + /* Check for denormalized, exponent should be zero. Left * + * operand was normalized, so extent (guard, round) was zero */ + if(!(underflowtrap = Is_underflowtrap_enabled()) && + result_exponent==0) goto underflow; + + /* Shift extension to complete one bit of normalization and + * update exponent. */ + Ext_leftshiftby1(extent); + + /* Discover first one bit to determine shift amount. Use a + * modified binary search. We have already shifted the result + * one position right and still not found a one so the remainder + * of the extension must be zero and simplifies rounding. */ + /* Scan bytes */ + while(Sgl_iszero_hiddenhigh7mantissa(result)) + { + Sgl_leftshiftby8(result); + if((result_exponent -= 8) <= 0 && !underflowtrap) + goto underflow; + } + /* Now narrow it down to the nibble */ + if(Sgl_iszero_hiddenhigh3mantissa(result)) + { + /* The lower nibble contains the normalizing one */ + Sgl_leftshiftby4(result); + if((result_exponent -= 4) <= 0 && !underflowtrap) + goto underflow; + } + /* Select case were first bit is set (already normalized) + * otherwise select the proper shift. */ + if((jumpsize = Sgl_hiddenhigh3mantissa(result)) > 7) + { + /* Already normalized */ + if(result_exponent <= 0) goto underflow; + Sgl_set_sign(result,/*using*/sign_save); + Sgl_set_exponent(result,/*using*/result_exponent); + *dstptr = result; + return(NOEXCEPTION); + } + Sgl_sethigh4bits(result,/*using*/sign_save); + switch(jumpsize) + { + case 1: + { + Sgl_leftshiftby3(result); + result_exponent -= 3; + break; + } + case 2: + case 3: + { + Sgl_leftshiftby2(result); + result_exponent -= 2; + break; + } + case 4: + case 5: + case 6: + case 7: + { + Sgl_leftshiftby1(result); + result_exponent -= 1; + break; + } + } + if(result_exponent > 0) + { + Sgl_set_exponent(result,/*using*/result_exponent); + *dstptr = result; /* Sign bit is already set */ + return(NOEXCEPTION); + } + /* Fixup potential underflows */ + underflow: + if(Is_underflowtrap_enabled()) + { + Sgl_set_sign(result,sign_save); + Sgl_setwrapped_exponent(result,result_exponent,unfl); + *dstptr = result; + /* inexact = FALSE */ + return(UNDERFLOWEXCEPTION); + } + /* + * Since we cannot get an inexact denormalized result, + * we can now return. + */ + Sgl_right_align(result,/*by*/(1-result_exponent),extent); + Sgl_clear_signexponent(result); + Sgl_set_sign(result,sign_save); + *dstptr = result; + return(NOEXCEPTION); + } /* end if(hidden...)... */ + /* Fall through and round */ + } /* end if(save >= 0)... */ + else + { + /* Add magnitudes */ + Sgl_addition(left,right,/*to*/result); + if(Sgl_isone_hiddenoverflow(result)) + { + /* Prenormalization required. */ + Sgl_rightshiftby1_withextent(result,extent,extent); + Sgl_arithrightshiftby1(result); + result_exponent++; + } /* end if hiddenoverflow... */ + } /* end else ...sub magnitudes... */ + + /* Round the result. If the extension is all zeros,then the result is + * exact. Otherwise round in the correct direction. No underflow is + * possible. If a postnormalization is necessary, then the mantissa is + * all zeros so no shift is needed. */ + round: + if(Ext_isnotzero(extent)) + { + inexact = TRUE; + switch(Rounding_mode()) + { + case ROUNDNEAREST: /* The default. */ + if(Ext_isone_sign(extent)) + { + /* at least 1/2 ulp */ + if(Ext_isnotzero_lower(extent) || + Sgl_isone_lowmantissa(result)) + { + /* either exactly half way and odd or more than 1/2ulp */ + Sgl_increment(result); + } + } + break; + + case ROUNDPLUS: + if(Sgl_iszero_sign(result)) + { + /* Round up positive results */ + Sgl_increment(result); + } + break; + + case ROUNDMINUS: + if(Sgl_isone_sign(result)) + { + /* Round down negative results */ + Sgl_increment(result); + } + + case ROUNDZERO:; + /* truncate is simple */ + } /* end switch... */ + if(Sgl_isone_hiddenoverflow(result)) result_exponent++; + } + if(result_exponent == SGL_INFINITY_EXPONENT) + { + /* Overflow */ + if(Is_overflowtrap_enabled()) + { + Sgl_setwrapped_exponent(result,result_exponent,ovfl); + *dstptr = result; + if (inexact) + if (Is_inexacttrap_enabled()) + return(OVERFLOWEXCEPTION | INEXACTEXCEPTION); + else Set_inexactflag(); + return(OVERFLOWEXCEPTION); + } + else + { + Set_overflowflag(); + inexact = TRUE; + Sgl_setoverflow(result); + } + } + else Sgl_set_exponent(result,result_exponent); + *dstptr = result; + if(inexact) + if(Is_inexacttrap_enabled()) return(INEXACTEXCEPTION); + else Set_inexactflag(); + return(NOEXCEPTION); + } |