### FILE="Main.annotation"
## Copyright:   Public domain.
## Filename:    SINGLE_PRECISION_SUBROUTINES.agc
## Purpose:     A section of Sunburst revision 37, or Shepatin revision 0.
##              It is part of an early development version of the software
##              for Apollo Guidance Computer (AGC) on the unmanned Lunar
##              Module (LM) flight Apollo 5. Sunburst 37 was the program
##              upon which Don Eyles's offline development program Shepatin
##              was based; the listing herein transcribed was actually for
##              the equivalent revision 0 of Shepatin.
##              This file is intended to be a faithful transcription, except
##              that the code format has been changed to conform to the
##              requirements of the yaYUL assembler rather than the
##              original YUL assembler.
## Reference:   pp. 985-987
## Assembler:   yaYUL
## Contact:     Ron Burkey <info@sandroid.org>.
## Website:     www.ibiblio.org/apollo/index.html
## Mod history: 2017-05-24 MAS  Created from Sunburst 120.
## 		2017-06-17 NV   Updated for Sunburst 37
##		2017-06-23 RSB	Proofed comment text with
##				octopus/ProoferComments.

## Page 985
		BLOCK		02
# SINGLE PRECISION SINE AND COSINE

SPCOS           AD              HALF                    # ARGUMENTS SCALED AT PI
SPSIN           TS              TEMK
                TCF             SPT
                CS              TEMK
SPT             DOUBLE
                TS              TEMK
                TCF             POLLEY
                XCH             TEMK
                INDEX           TEMK
                AD              LIMITS
                COM
                AD              TEMK
                TS              TEMK
                TCF             POLLEY
                TCF             ARG90
POLLEY          EXTEND
                MP              TEMK
                TS              SQ
                EXTEND
                MP              C5/2
                AD              C3/2
                EXTEND
                MP              SQ
                AD              C1/2
                EXTEND
                MP              TEMK
                DDOUBL
                TS              TEMK
                TC              Q
ARG90           INDEX           A
                CS              LIMITS
                TC              Q                       # RESULT SCALED AT 1
C1/2            DEC             .7853134
C3/2            DEC             -.3216146
C5/2            DEC             .0363551
## Page 986
# ENTER WITH ARGUMENT IN A, EXIT WITH ROOT IN A.  IF GIVEN A NEGATIVE ARGUMENT, THE RETURN SKIPS WITH CCS RESULT.
# MINUS ZERO RETURNS LIKE PLUS ZERO.
# MAXIMUM ERROR IN ANSWER IS NO GREATER THAN 2 BITS.
# INTERRUPT PROGRAMS USING SPROOT MUST SAVE AND RESTORE SR.



SPROOT          TS              SQRARG                  # ENTER WITH C(A) = Y
                CCS             A
                TCF             POSARG                  # IF PNZ, CONTINUE
                TC              Q                       # RETURN WITH 0 FOR +0
                INCR            Q
                TC              Q                       # RETURN WITH 0 FOR -0

POSARG          EXTEND
                QXCH            ROOTRET                 # WILL BE CALLING SPROOT1
                AD              63/64+1                 # B(A) = Y - 1
                OVSK
                TCF             SPROOT2
                XCH             SQRARG                  # ARG JUGGLING

SPROOT3         TS              SQRARG
                TS              SR                      # C(A) = Y
                XCH             SR                      # (LOSE 1 BIT)
                TS              HALFY                   # HALFY = Y/2
                AD              -1/8                    # FORM Y/2 - 1/8
                CCS             A                       # TEST FOR FIRST GUESS
                AD              5/8+1                   # Y .G. 1/4, X = Y/2 + 1/2
                TC              HIGUESS                 # +0 IMPOSSIBLE FROM ADDITION
                NOOP                                    # Y .LE. 1/4, X/2 = Y + 1/16
                CAF             BIT11                   # 1/16
                AD              SQRARG                  # SQRARG = Y
                DOUBLE                                  # X FROM X/2
HIGUESS         TC              SPROOT1
                TC              SPROOT1                 # ITERATE TWICE
                XCH             ROOTRET                 # SAVE ANSWER AND GET Q
                CCS             A
                XCH             ROOTRET                 # NO SHIFT NEEDED
                TC              ROOTBCK
                XCH             ROOTRET                 # Q NEG, SHIFT RIGHT THREE
                EXTEND
                MP              BIT12                   # EXP -3
ROOTBCK         INDEX           ROOTRET                 # ROOTRET = Q - 1
                TC              1                       # RETURN, C(A) = SQRT(Y)

SPROOT1         XCH             SR                      # SR = X/2
                CS              HALFY                   # NEWTON ITER  X = X/2 + (Y/2 / X/2) / 2
                ZL
                EXTEND
                DV              SR                      # C(SR) = X/2 DV DOES NOT EDIT
## Page 987
                XCH             SR
                EXTEND
                SU              SR
                TC              Q                       # C(A) = X (NEXT)

SPROOT2         CS              ROOTRET                 # SET RETURN Q NEG, AS FLAG
                TS              ROOTRET
                CAF             BIT7                    # SHIFT FOR SIGNIFCANCE
                EXTEND
                MP              SQRARG
                CA              L                       # B(A) = 0
                TC              SPROOT3

-1/8            OCTAL           73777
5/8+1           OCTAL           24001
63/64+1         OCTAL           37401