| // 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); |
| } |
