add hexdump

.gitignore

@@ -3,3 +3,4 @@
 /cat
 /printstack
 /env
+/hexdump

Makefile

@@ -5,7 +5,7 @@ LD = $(TARGET)-ld
 .SUFFIXES:
 
 .PHONY: all
-all: true false cat env
+all: true false cat env hexdump
 #all: echo
 
 %: %.o

hexdump.s

@@ -0,0 +1,175 @@
+.globl _start
+.option rvc # enable compressed instructions
+
+.data
+writebuf: .ascii "00000000: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 | ................\n"
+.equ hexstart, 10
+.equ hexend, hexstart+3*16
+.equ charstart, hexend+3
+.equ linelen, (. - writebuf)
+.equ readlen, 16
+readbuf: .zero readlen
+
+.text
+_start:
+    # set up the gp register so that relaxed loads work
+    .option push
+    .option norelax
+    la gp, __global_pointer$
+    .option pop
+
+    # fd in s6
+    # data offset in s7
+    li s6, 0
+    li s7, 0 #0xabad1dea
+
+
+loop:
+    li a7, 63      # sys_read
+    mv a0, s6      # fd
+    la a1, readbuf # pointer to buffer
+    li a2, readlen  # size of buffer
+    ecall
+    #li a0, 0
+
+    # return in a0
+    #   negative => error code
+    #   positive => number of byte read
+    #   zero     => end of input
+    bltz a0, error
+    beqz a0, done
+    
+    li t5, 10
+
+    la s0, writebuf
+
+    .macro hexnibble src, shift, dest
+    slli t1, \src, (64-\shift-4) # put high nibble of s7 in t1
+    srli t1, t1, 64-4
+    addi t2, t1, 0x30 # convert to decimal digit
+    bgt t5, t1, 0f # if digit >= 10, use switch to alpha
+    addi t2, t1, 0x61-10
+0:
+    # copy digit to writebuf
+    sb t2, \dest
+    .endm
+
+    .macro hexbyte src, shift, dest
+    hexnibble \src, (\shift+4), \dest
+    hexnibble \src, \shift, 1+\dest
+    .endm
+
+    hexbyte s7, 24, 0(s0)
+    hexbyte s7, 16, 2(s0)
+    hexbyte s7, 8, 4(s0)
+    hexbyte s7, 0, 6(s0)
+
+    la s1, readbuf
+
+    # it's perfectly fine to process more
+    # bytes than we read here, since the buffer
+    # sizes are both fixed
+    .macro inpbyte srcindex, dstindex
+    lbu t0, \srcindex(s1)
+    hexbyte t0, 0, \dstindex(s0)
+    .endm
+
+    # TODO: load 8 bytes at a time
+    #  (need a way to check endianness)
+    inpbyte 0, 10
+    inpbyte 1, 13
+    inpbyte 2, 16
+    inpbyte 3, 19
+    inpbyte 4, 22
+    inpbyte 5, 25
+    inpbyte 6, 28
+    inpbyte 7, 31
+
+    inpbyte 8, 35
+    inpbyte 9, 38
+    inpbyte 10, 41
+    inpbyte 11, 44
+    inpbyte 12, 47
+    inpbyte 13, 50
+    inpbyte 14, 53
+    inpbyte 15, 56
+
+
+    li t0, 0
+    li t4, 0x7e-0x20
+    # the ascii printable range is 0x20-0x7e
+    #
+    #      0123456789ABCDEF
+    #   20  !"#$%&'()*+,-./
+    #   30 0123456789:;<=>?
+    #   40 @ABCDEFGHIJKLMNO
+    #   50 PQRSTUVWXYZ[\]^_
+    #   60 `abcdefghijklmno
+    #   70 pqrstuvwxyz{|}~
+printable_loop:
+    add t1, s1, t0
+    lbu t2, 0(t1)
+    addi t3, t2, -0x20
+    bleu t3, t4, 0f
+    li t2, 0x2e # '.' 
+    0:
+    add t1, s0, t0
+    sb t2, 61(t1)
+    addi t0, t0, 1
+    blt t0, a0, printable_loop
+
+    li t0, readlen
+    blt a0, t0, fixup
+
+    mv s0, a0 # save length read
+    add s7, s7, s0 # file offset += s0
+
+    li a7, 64      # sys_write
+    li a0, 1       # fd = stdout
+    la a1, writebuf     # pointer to string
+    li a2, linelen      # size of data
+    ecall
+
+    bltz a0, error
+    j loop
+
+fixup:
+    # we read <16 bytes, so we need to 
+    # 1) replace the hex bytes >a0 with spaces
+    # 2) adjust the line length
+    # 3) print it
+    
+    add t0, a0, a0 # t0 = len*3
+    add t0, t0, a0
+    addi t0, t0, hexstart
+    add t0, s0, t0
+    addi t1, s0, hexend
+    li t2, 0x20
+1:
+    sb t2, 0(t0)
+    addi t0, t0, 1
+    blt t0, t1, 1b
+
+    addi t0, a0, charstart
+    add t1, t0, s0
+    li t2, 0xa # \n
+    sb t2, 0(t1)
+    li a7, 64      # sys_write
+    li a0, 1       # fd = stdout
+    la a1, writebuf     # pointer to string
+    addi a2, t0, 1      # size of data
+    ecall
+    bltz a0, error
+    j done
+
+error:
+    li a7, 93 # exit
+    li a0, 1
+    ecall
+    
+done:
+    li a7, 93 # exit
+    li a0, 0
+    ecall
+
+