Texas Instruments TI89 Developer Guide - Page 467
round12_err, Example, round14
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Appendix A: System Routines - Direct Floating Point Operations 425 round12_err (continued) Example: The zoom trig on the grapher sets up the range variables depending on the degrees/radians setting and the number of pixels in the X direction of the graph as shown in this example. The xscl factor is rounded to 14 digits using round14 but the xmin and xmax variables are rounded to 12 digits using round12_err. void SysVarStore( short sysNum, BCD16 value ) { Access_AMS_Global_Variables; EStackIndex saveTop = top_estack; BYTE tag[2]; tag[1] = SYSVAR_TAG; tag[0] = sysNum; push_Float( value ); VarStore( tag+1, STOF_ESI, 0, top_estack ); top_estack = saveTop; } void GZ_Trig( void ) { Access_AMS_Global_Variables; short xp; BCD16 *fr, TempF; fr = gr_active->rngp; xp = gr_active->xmaxpix; if (IS_DEGREES) { SysVarStore( SV_DELTAX, 7.5 ); SysVarStore( SV_XSCL, FLOATTAB[FPI_90] ); } else { SysVarStore( SV_DELTAX, FLOATTAB[FPI_PIDIV24] ); SysVarStore( SV_XSCL, round14(FLOATTAB[FPI_PIDIV2]) ); } TempF = -(fr[GR_DELTAX] * xp) / FLOATTAB [FPI_2]; SysVarStore( SV_XMIN, round12_err( TempF, ER_RANGE ) ); SysVarStore( SV_XMAX, round12_err(fr[GR_DELTAX] * xp + TempF, ER_RANGE) ); SysVarStore( SV_YMIN, -4.0 ); SysVarStore( SV_YMAX, 4.0 ); SysVarStore( SV_YSCL, 0.5 ); GT_Regraph(); } TI-89 / TI-92 Plus Developer Guide Not for Distribution Beta Version January 26, 2001
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