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Length: 2457 (0x999)
Types: TextFile
Notes: UNIX file
Names: »ddiv.s«
└─⟦f27320a65⟧ Bits:30001972 Commodore 900 hard disk image with partial source code
└─⟦f4b8d8c84⟧ UNIX Filesystem
└─ ⟦this⟧ »libc/crt/ddiv.s«
/ floating point package for segmented z-8001 / timothy s. murphy 10/84 / IEEE format / double: 63 62 52 51 0 / sign bin exp +1022 fraction (missing hi bit) / float: 31 30 23 22 0 / sign bin exp +126 fraction (missing hi bit) / .globl SS .globl drdiv, dldiv / / divide a/b result in rq4 / see knuth "art of computer programming" vol.2 / for explanation of double precision divide / life is complicated further by the lack of unsigned multply & divide / / drdiv( da, db) / dldiv( da, &db) drdiv: lda rr2, SS|12(r15) jr un, 0f dldiv: ldl rr2, SS|12(r15) 0: sub r15, $16 ldm (rr14), r6, $8 ld r0, SS|20(r15) ldl rr4, SS|22(r15) ld r6, SS|26(r15) sub r7, r7 ld r8, (rr2) ldl rr12, rr2(2) ld r10, rr2(6) sub r11, r11 ld r1, $32768 ld r9, r1 and r1, r0 xor r0, r1 cp r0, $16 jr lt, retz and r9, r8 xor r8, r9 xor r1, r9 / result sign cp r8, $16 jr lt, retinf cp r0, $2047*16 jr ge, retinf cp r8, $2047*16 jr ge, retz ldb rl1, $4 / form exponents, fractions 0: srl r0 rrc r4 rrc r5 rrc r6 rrc r7 srl r8 rrc r12 rrc r13 rrc r10 rrc r11 dbjnz rl1, 0b setflg C rrc r4 rrc r5 rrc r6 rrc r7 setflg C rrc r12 rrc r13 rrc r10 rrc r11 sub r0, r8 add r0, $1023 jr le, retz / exp will only get smaller ▶08◀▶08◀▶08◀▶08◀▶08◀ cp r0, $2048 jr ge, retinf / by at most 1 srll rr12 / make divisor positive rrc r10 rrc r11 srll rr4 / make quotient defined & positive rrc r6 rrc r7 srll rr4 rrc r6 rrc r7 srll rr4 rrc r6 rrc r7 divl rq4, rr12 / rr6 = good approx to hi part of quotient / we adjust using 1st term of power series / as in knuth srll rr10 ld r9, $-1 com r10 neg r11 sbc r10, r9 multl rq8, rr6 / - vl x ww▶08◀m ( cf knuth) srll rr4, $1 addl rr8, rr4 / + r ( no ovflw since opp signs) sral rr8 rrc r10 rrc r11 divl rq8, rr12 extsl rq8 slll rr10 / undo shifts for positiveness rlc r9 slll rr10 rlc r9 addl rr8, rr6 / form quotient of fractions slll rr10 rlc r9 rlc r8 slll rr10 rlc r9 rlc r8 jr c, 0f slll rr10 rlc r9 rlc r8 dec r0 jr le, retz 0: cp r0, $2047 jr ge, retinf slll rr10 rlc r9 rlc r8 rlc r0 slll rr10 rlc r9 rlc r8 rlc r0 slll rr10 rlc r9 rlc r8 rlc r0 slll rr10 rlc r9 rlc r8 rlc r0 or r0, r1 ld r1, r8 ld r2, r9 ld r3, r10 9: ldm r6, (rr14), $8 inc r15, $16 ret retz: subl rr0, rr0 subl rr2, rr2 jr un, 9b retinf: ld r0, $2047*16 or r0, r1 sub r1, r1 subl rr2, rr2 jr un, 9b