implement u-format for JAL

1 files changed, 13 insertions, 0 deletions

diff --git a/riscv.py b/riscv.py
index b2af4cc..c0d5a15 100644
--- a/riscv.py
+++ b/riscv.py
@@ -29,3 +29,16 @@ def format_u(op, rd, imm20):
   b2 = (imm20 >> 4) & 0xff
   b3 =  imm20 >> 12
   return [(b0,), (b1,), (b2,), (b3,)]
+
+def format_j(op, rd, imm):
+  # opcode[7] rd[5] imm19:12[8] imm11[1] imm10:1[10] imm20[1]
+  imm12 = (imm >> 11) & 0xff
+  imm11 = (imm >> 12) & 0x1
+  imm1 = imm & 0x3ff
+  imm20 = imm >> 19
+
+  b0 =    (rd & 0x1) << 7 | op      # rd[1] op[7:0]
+  b1 = (imm12 & 0xf) << 4 | rd >> 1 # imm[15:12] rd[5:2]
+  b2 = (imm1 << 5) & 0xe0 | imm11 << 4 | (imm12 >> 4)          # imm[3:1] imm[11] imm[19:16]
+  b3 = imm20 << 7 | imm1 >> 3
+  return [(b0,), (b1,), (b2,), (b3,)]