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/* Read a number of words from the ATA data port
 *
 * Utilises line bursts, assumes there is at least one full line to copy.
 *
 * Arguments:
 *   (4,%sp) - buffer address
 *   (8,%sp) - word count
 *
 * Register usage:
 *   %a0 - current address
 *   %a1 - end address
 *   %a2 - ata port
 *   %d0 - scratch
 *   %d1 - shift count
 *   %d2-%d6 - read buffers
 *
 *   %d7 - byte swap scrach register
 *   %a3 - byte swap mask
 */

copy_read_sectors:
    lea.l   (-32, %sp), %sp
    movem.l %d2-%d7/%a2-%a3, (%sp)
    movem.l (36, %sp), %a0-%a1
    add.l   %a1, %a1
    add.l   %a0, %a1
    lea.l   .ata_port, %a2
    lea.l   .swapmask, %a3

    move.l  %a0, %d0
    btst.l  #0, %d0         /* 16-bit aligned? */
    jeq     .r_aligned      /* yes, do word copy */

    /* not 16-bit aligned */
    subq.l  #1, %a1         /* last byte is done unconditionally */
    moveq.l #24, %d1        /* preload shift count */

    move.w  (%a2), %d2      /* load initial word */
    move.b  %d2, (%a0)+     /* write high byte of it, aligns dest addr */
                            /* we have byte swapped */
    lsr.l #8, %d2

    btst.l  #1, %d0         /* longword aligned? (testing old d0 value!) */
    bne.b   .r_end_u_w1     /* yes, skip leading word handling */

    swap    %d2             /* move initial word up */
    move.w  (%a2), %d2      /* combine with second word */

    /* byte swap d2 */
    move.l  %a3, %d7        /* d7 = 0x00FF00FF */
    and.l   %d2, %d7        /* d7 = .B.D */
    eor.l   %d7, %d2        /* d2 = A.C. */
    lsl.l   #8, %d7         /* d7 = B.D. */
    lsr.l   #8, %d2         /* d2 = .A.C */
    or.l    %d7, %d2        /* d2 = BADC */

    move.l  %d2, %d3
    lsr.l   #8, %d3
    move.w  %d3, (%a0)+     /* write bytes 2 and 3 as word */

.r_end_u_w1:
    moveq.l #12, %d0
    add.l   %a0, %d0
    and.l   #0xFFFFFFF0,%d0 /* d0 == first line bound */
    cmp.l   %a0, %d0        /* any leading longwords? */
    bls.b   .r_end_u_l1     /* no: skip loop */

.r_loop_u_l1:
    move.w  (%a2), %d3      /* load first word */
    swap    %d3             /* move to upper 16 bit */
    move.w  (%a2), %d3      /* load second word */

    /* byte swap d3 */
    move.l  %a3, %d7        /* d7 = 0x00FF00FF */
    and.l   %d3, %d7        /* d7 = .B.D */
    eor.l   %d7, %d3        /* d3 = A.C. */
    lsl.l   #8, %d7         /* d7 = B.D. */
    lsr.l   #8, %d3         /* d3 = .A.C */
    or.l    %d7, %d3        /* d3 = BADC */

    move.l  %d3, %d4

    lsl.l   %d1, %d2
    lsr.l   #8, %d3
    or.l    %d3, %d2        /* combine old low byte with new top 3 bytes */
    move.l  %d2, (%a0)+     /* store as long */
    move.l  %d4, %d2
    cmp.l   %a0, %d0        /* run up to first line bound */
    bhi.b   .r_loop_u_l1

.r_end_u_l1:
    lea.l   (-14, %a1), %a1 /* adjust end addr. to 16 bytes/pass */

.r_loop_u_line:
    move.w  (%a2), %d3      /* load 1st word */
    swap    %d3             /* move to upper 16 bit */
    move.w  (%a2), %d3      /* load 2nd word */

    /* byte swap d3 */
    move.l  %a3, %d7        /* d7 = 0x00FF00FF */
    and.l   %d3, %d7        /* d7 = .B.D */
    eor.l   %d7, %d3        /* d3 = A.C. */
    lsl.l   #8, %d7         /* d7 = B.D. */
    lsr.l   #8, %d3         /* d3 = .A.C */
    or.l    %d7, %d3        /* d3 = BADC */

    move.l  %d3, %d0

    lsl.l   %d1, %d2
    lsr.l   #8, %d0
    or.l    %d0, %d2        /* combine old low byte with new top 3 bytes */
    move.w  (%a2), %d4      /* load 3rd word */
    swap    %d4             /* move to upper 16 bit */
    move.w  (%a2), %d4      /* load 4th word */

    /* byte swap d4 */
    move.l  %a3, %d7        /* d7 = 0x00FF00FF */
    and.l   %d4, %d7        /* d7 = .B.D */
    eor.l   %d7, %d4        /* d4 = A.C. */
    lsl.l   #8, %d7         /* d7 = B.D. */
    lsr.l   #8, %d4         /* d4 = .A.C */
    or.l    %d7, %d4        /* d4 = BADC */

    move.l  %d4, %d0
    lsl.l   %d1, %d3
    lsr.l   #8, %d0
    or.l    %d0, %d3        /* combine old low byte with new top 3 bytes */
    move.w  (%a2), %d5      /* load 5th word */
    swap    %d5             /* move to upper 16 bit */
    move.w  (%a2), %d5      /* load 6th word */

    /* byte swap d5 */
    move.l  %a3, %d7        /* d7 = 0x00FF00FF */
    and.l   %d5, %d7        /* d7 = .B.D */
    eor.l   %d7, %d5        /* d5 = A.C. */
    lsl.l   #8, %d7         /* d7 = B.D. */
    lsr.l   #8, %d5         /* d5 = .A.C */
    or.l    %d7, %d5        /* d5 = BADC */

    move.l  %d5, %d0
    lsl.l   %d1, %d4
    lsr.l   #8, %d0
    or.l    %d0, %d4        /* combine old low byte with new top 3 bytes */
    move.w  (%a2), %d6      /* load 7th word */
    swap    %d6             /* move to upper 16 bit */
    move.w  (%a2), %d6      /* load 8th word */

    /* byte swap d6 */
    move.l  %a3, %d7        /* d7 = 0x00FF00FF */
    and.l   %d6, %d7        /* d7 = .B.D */
    eor.l   %d7, %d6        /* d6 = A.C. */
    lsl.l   #8, %d7         /* d7 = B.D. */
    lsr.l   #8, %d6         /* d6 = .A.C */
    or.l    %d7, %d6        /* d6 = BADC */

    move.l  %d6, %d0
    lsl.l   %d1, %d5
    lsr.l   #8, %d0
    or.l    %d0, %d5        /* combine old low byte with new top 3 bytes */
    movem.l %d2-%d5, (%a0)  /* store line */
    lea.l   (16, %a0), %a0
    move.l  %d6, %d2
    cmp.l   %a0, %a1        /* run up to last line bound */
    bhi.b   .r_loop_u_line

    lea.l   (12, %a1), %a1  /* readjust for longword loop */
    cmp.l   %a0, %a1        /* any trailing longwords? */
    bls.b   .r_end_u_l2     /* no: skip loop */

.r_loop_u_l2:
    move.w  (%a2), %d3      /* load first word */
    swap    %d3             /* move to upper 16 bit */
    move.w  (%a2), %d3      /* load second word */

    /* byte swap d3 */
    move.l  %a3, %d7        /* d7 = 0x00FF00FF */
    and.l   %d3, %d7        /* d7 = .B.D */
    eor.l   %d7, %d3        /* d3 = A.C. */
    lsl.l   #8, %d7         /* d7 = B.D. */
    lsr.l   #8, %d3         /* d3 = .A.C */
    or.l    %d7, %d3        /* d3 = BADC */

    move.l  %d3, %d4
    lsl.l   %d1, %d2
    lsr.l   #8, %d3
    or.l    %d3, %d2        /* combine old low byte with new top 3 bytes */
    move.l  %d2, (%a0)+     /* store as long */
    move.l  %d4, %d2
    cmp.l   %a0, %a1        /* run up to last long bound */
    bhi.b   .r_loop_u_l2

.r_end_u_l2:
    addq.l  #2, %a1         /* back to final end address */
    cmp.l   %a0, %a1        /* one word left? */
    bls.b   .r_end_u_w2

    move.w  (%a2), %d3
    move.l  %d3, %d0
    lsl.l   #8, %d2
    and.l   #0xff, %d0
    or.l    %d0, %d2

    move.w  %d2, (%a0)+     /* write bytes 2 and 3 as word */

    move.l  %d3, %d2
    lsr.l   #8, %d2
.r_end_u_w2:
    move.b  %d2, (%a0)+     /* store final byte */
    bra.w   .r_exit

    /* 16-bit aligned */
.r_aligned:
    btst.l  #1, %d0         /* longword aligned? */
    beq.b   .r_end_a_w1     /* yes, skip leading word handling */

    /* copy initial word */
    /* initial word has to be swapped */
    move.w  (%a2), %d7
    move.b  %d7, (%a0)+
    lsr.l   #8, %d7
    move.b  %d7, (%a0)+

.r_end_a_w1:
    moveq.l #12, %d0
    add.l   %a0, %d0
    and.l   #0xFFFFFFF0,%d0 /* d0 == first line bound */
    cmp.l   %a0, %d0        /* any leading longwords? */
    bls.b   .r_end_a_l1     /* no: skip loop */

.r_loop_a_l1:
    move.w  (%a2), %d1      /* load first word */
    swap    %d1             /* move it to upper 16 bits */
    move.w  (%a2), %d1      /* load second word */

    /* byte swap d1 */
    move.l  %a3, %d7        /* d7 = 0x00FF00FF */
    and.l   %d1, %d7        /* d7 = .B.D */
    eor.l   %d7, %d1        /* d1 = A.C. */
    lsl.l   #8, %d7         /* d7 = B.D. */
    lsr.l   #8, %d1         /* d1 = .A.C */
    or.l    %d7, %d1        /* d1 = BADC */

    move.l  %d1, (%a0)+     /* store as long */
    cmp.l   %a0, %d0        /* run up to first line bound */
    bhi.b   .r_loop_a_l1

.r_end_a_l1:
    lea.l   (-14, %a1), %a1 /* adjust end addr. to 16 bytes/pass */

.r_loop_a_line:
    move.w  (%a2), %d0      /* load 1st word */
    swap    %d0             /* move it to upper 16 bits */
    move.w  (%a2), %d0      /* load 2nd word */

    /* byte swap d0 */
    move.l  %a3, %d7        /* d7 = 0x00FF00FF */
    and.l   %d0, %d7        /* d7 = .B.D */
    eor.l   %d7, %d0        /* d0 = A.C. */
    lsl.l   #8, %d7         /* d7 = B.D. */
    lsr.l   #8, %d0         /* d0 = .A.C */
    or.l    %d7, %d0        /* d0 = BADC */

    move.w  (%a2), %d1      /* load 3rd word */
    swap    %d1             /* move it to upper 16 bits */
    move.w  (%a2), %d1      /* load 4th word */

    /* byte swap d1 */
    move.l  %a3, %d7        /* d7 = 0x00FF00FF */
    and.l   %d1, %d7        /* d7 = .B.D */
    eor.l   %d7, %d1        /* d1 = A.C. */
    lsl.l   #8, %d7         /* d7 = B.D. */
    lsr.l   #8, %d1         /* d1 = .A.C */
    or.l    %d7, %d1        /* d1 = BADC */

    move.w  (%a2), %d2      /* load 5th word */
    swap    %d2             /* move it to upper 16 bits */
    move.w  (%a2), %d2      /* load 6th word */

    /* byte swap d2 */
    move.l  %a3, %d7        /* d7 = 0x00FF00FF */
    and.l   %d2, %d7        /* d7 = .B.D */
    eor.l   %d7, %d2        /* d2 = A.C. */
    lsl.l   #8, %d7         /* d7 = B.D. */
    lsr.l   #8, %d2         /* d2 = .A.C */
    or.l    %d7, %d2        /* d2 = BADC */

    move.w  (%a2), %d3      /* load 7th word */
    swap    %d3             /* move it to upper 16 bits */
    move.w  (%a2), %d3      /* load 8th word */

    /* byte swap d3 */
    move.l  %a3, %d7        /* d7 = 0x00FF00FF */
    and.l   %d3, %d7        /* d7 = .B.D */
    eor.l   %d7, %d3        /* d3 = A.C. */
    lsl.l   #8, %d7         /* d7 = B.D. */
    lsr.l   #8, %d3         /* d3 = .A.C */
    or.l    %d7, %d3        /* d3 = BADC */

    movem.l %d0-%d3, (%a0)  /* store line */
    lea.l   (16, %a0), %a0
    cmp.l   %a0, %a1        /* run up to last line bound */
    bhi.b   .r_loop_a_line

    lea.l   (12, %a1), %a1  /* readjust for longword loop */
    cmp.l   %a0, %a1        /* any trailing longwords? */
    bls.b   .r_end_a_l2     /* no: skip loop */

.r_loop_a_l2:
    move.w  (%a2), %d1      /* read first word */
    swap    %d1             /* move it to upper 16 bits */
    move.w  (%a2), %d1      /* read second word */

    /* byte swap d1 */
    move.l  %a3, %d7        /* d7 = 0x00FF00FF */
    and.l   %d1, %d7        /* d7 = .B.D */
    eor.l   %d7, %d1        /* d1 = A.C. */
    lsl.l   #8, %d7         /* d7 = B.D. */
    lsr.l   #8, %d1         /* d1 = .A.C */
    or.l    %d7, %d1        /* d1 = BADC */

    move.l  %d1, (%a0)+     /* store as long */
    cmp.l   %a0, %a1        /* run up to last long bound */
    bhi.b   .r_loop_a_l2

.r_end_a_l2:
    addq.l  #2, %a1         /* back to final end address */
    cmp.l   %a0, %a1        /* one word left? */
    bls.b   .r_end_a_w2

    /* copy final word */
    /* final word has to be swapped */
    move.w (%a2), %d7
    move.b %d7, (%a0)+
    lsr.l  #8, %d7
    move.b %d7, (%a0)+

.r_end_a_w2:

.r_exit:
    movem.l (%sp), %d2-%d7/%a2-%a3
    lea.l   (32, %sp), %sp
    rts