diff --git a/Makefile b/Makefile
index b345799..ef7e141 100644
--- a/Makefile
+++ b/Makefile
@@ -15,6 +15,7 @@ all: true false cat env hexdump
 	$(AS) -o $@ $<
 
 prtest: prtest.o lib/printregs.o lib/hex.o
+sorttest: lib/sort.o
 
 .PHONY: test
 test:
diff --git a/lib/sort.s b/lib/sort.s
new file mode 100644
index 0000000..7351bd6
--- /dev/null
+++ b/lib/sort.s
@@ -0,0 +1,152 @@
+.global sort
+
+# a0 = pointer to array to be sorted
+# a1 = length of array (signed)
+# a2 = element size (unsigned)
+# a3 - comparison function
+# a4 - context
+sort:
+    # insertion sort
+    # for i = 0 to n-1
+    #    for j = i downto 0
+    #         if a[j-1] > a[j]
+    #             swap a[j-1], a[j]
+
+    # i = 0
+    # for n-1 downto 0
+    #    i += esize
+    #    j = i
+    #    while j > 0:
+    #         if cmp(j-esize, j) > 0
+    #             swap(j-esize, j)
+    #         else
+    #            break
+    #         j -= esize
+    #
+
+    # bail early if n <= 1
+    li  t0, 1
+    bgt a1, t0, 0f
+    li  a0, 0
+    ret
+  0:
+
+    # check if n*esize overflows or is negative
+    mulhu t1, a1, a2
+    beqz  t1, 0f
+    li a0, -1
+    ret
+  0:
+
+    sd ra, -1*8(sp)
+    sd s0, -2*8(sp)
+    sd s1, -3*8(sp)
+    sd s2, -4*8(sp)
+    sd s3, -5*8(sp)
+    sd s4, -6*8(sp)
+    sd s5, -7*8(sp)
+    sd s6, -8*8(sp)
+    addi sp, sp, -8*8
+
+    mv s0, a2 # pointer to element i - base
+    # s1 is pointer to element j - base
+    mv s2, a0 # base pointer
+    mv s3, a1 # array len
+    mv s4, a2 # element size
+    mv s5, a3 # cmp
+    mv s6, a4 # context
+
+    # we know we have at least 2 elements,
+    # so no check necessary at the top of the loop
+    addi s3, s3, -1
+.Louter.top:
+    # i += esize
+    # j = i
+    add s0, s0, s4
+    mv s1, s0
+
+.Linner.top:
+    add a1, s1, s2 # create pointers
+    sub a0, a1, s4
+    mv a2, s6
+    jalr s5 # cmp
+    #li a0, 1
+    blez a0, .Lcmp.less
+
+.Lcmp.greater:
+.Lswap:
+    add a1, s1, s2
+    sub a0, a1, s4
+    mv a2, s4
+    call swap
+
+.Linner.step:
+    sub s1, s1, s4
+    bnez s1, .Linner.top
+
+.Lcmp.less:
+.Louter.step:
+    addi s3, s3, -1 # n -= 1
+    bnez s3, .Louter.top
+
+.Lreturn:
+    addi sp, sp, 8*8
+    ld ra, -1*8(sp)
+    ld s0, -2*8(sp)
+    ld s1, -3*8(sp)
+    ld s2, -4*8(sp)
+    ld s3, -5*8(sp)
+    ld s4, -6*8(sp)
+    ld s5, -7*8(sp)
+    ld s6, -8*8(sp)
+    ret
+
+.Lerror:
+    li a0, -1
+    j .Lreturn
+
+swap:
+    # TODO: larger things
+    li t0, 8
+    bgtu a2, t0, bigswap
+    beq a2, t0, swap8
+    li t0, 4
+    beq a2, t0, swap4
+    li t0, 2
+    beq a2, t0, swap2
+    li t0, 1
+    beq a2, t0, swap1
+    beqz a2, .Lret
+
+    # TODO: weird size: 0, 3, 5, 6, 7
+.Lret:
+    ret
+    
+swap8:
+    ld t0, (a0)
+    ld t1, (a1)
+    sd t1, (a0)
+    sd t0, (a1)
+    ret
+swap4:
+    lwu t0, (a0)
+    lwu t1, (a1)
+    sw t1, (a0)
+    sw t0, (a1)
+    ret
+swap2:
+    lhu t0, (a0)
+    lhu t1, (a1)
+    sh t1, (a0)
+    sh t0, (a1)
+    ret
+swap1:
+    lbu t0, (a0)
+    lbu t1, (a1)
+    sb t1, (a0)
+    sb t0, (a1)
+    ret
+
+bigswap:
+    # TODO
+    ret
diff --git a/sorttest.s b/sorttest.s
new file mode 100644
index 0000000..f7560f1
--- /dev/null
+++ b/sorttest.s
@@ -0,0 +1,51 @@
+.globl _start
+.extern sort
+
+.data
+
+array:
+    .ascii "ABC "
+    .ascii "ZZZ "
+    .ascii "CCC "
+    .ascii "BBB "
+    .ascii "DED "
+    .ascii "\n"
+.equ len, (.) - array
+
+.text
+
+_start:
+    .option push
+    .option norelax
+    la gp, __global_pointer$
+    .option pop
+
+    li a7, 64
+    li a0, 1
+    la a1, array
+    li a2, len
+    ecall
+
+    la a0, array
+    li a1, len/4
+    li a2, 4
+    la a3, cmp
+    li a4, 0
+
+    call sort
+
+    li a7, 64
+    li a0, 1
+    la a1, array
+    li a2, len
+    ecall
+
+    li a7, 93 # sys_exit
+    li a0, 0
+    ecall
+
+cmp:
+    lw t0, (a0)
+    lw t1, (a1)
+    sgtu a0, t0, t1
+    ret