alu_bin.c File Reference

Binary and decimal (unpacked) arithmetic helpers for the GE-120/130. More...

#include "alu_bin.h"
#include <string.h>

Go to the source code of this file.

Functions
static uint8_t	field_byte (const struct ge *ge, uint16_t base_addr, uint8_t len, uint8_t pos)
	Read one byte from a multi-byte big-endian field at position pos (0 = least-significant byte = rightmost, len-1 = most-significant).
static void	field_byte_set (struct ge *ge, uint16_t base_addr, uint8_t len, uint8_t pos, uint8_t val)
	Write one byte into a multi-byte big-endian field.
void	alu_ab (struct ge *ge, uint16_t a_addr, uint8_t a_len, uint16_t b_addr, uint8_t b_len)
	AB – Add Binary (opcode 0xFE).
void	alu_sb (struct ge *ge, uint16_t a_addr, uint8_t a_len, uint16_t b_addr, uint8_t b_len)
	SB – Subtract Binary (opcode 0xFF).
static uint8_t	dec_digit (const struct ge *ge, uint16_t base_addr, uint8_t len, uint8_t pos)
void	alu_ad (struct ge *ge, uint16_t a_addr, uint8_t a_len, uint16_t b_addr, uint8_t b_len)
	AD – Add Decimal (opcode 0xFA).
void	alu_sd (struct ge *ge, uint16_t a_addr, uint8_t a_len, uint16_t b_addr, uint8_t b_len)
	SD – Subtract Decimal (opcode 0xFB).

Detailed Description

Binary and decimal (unpacked) arithmetic helpers for the GE-120/130.

Manual references: cpu_6.txt §5.5.1 – Decimal arithmetics (AD, SD) cpu_6.txt §5.5.2 – Binary arithmetics (AB, SB) cpu_6.txt §5.10.2 – Qualitative results summary table

Operand model (§5.5.1 / §5.5.2): addr points to the RIGHTMOST (least-significant) byte. The field occupies memory[addr - len + 1 .. addr]. All operations are performed right-to-left (LSD first).

Length rules (verified from manual text): If L2 > L1: truncate operand 2 to L1 (treat as if L2 = L1). If L2 < L1: zero-extend operand 2 on the left.

CC encoding (§5.10.2): cc = (FA04 << 1) | FA05 Stored by alu_set_cc() into ffFI bits 4 (hi) and 5 (lo).

Definition in file alu_bin.c.

Function Documentation

alu_ab()

void alu_ab	(	struct ge *	ge,
		uint16_t	a_addr,
		uint8_t	a_len,
		uint16_t	b_addr,
		uint8_t	b_len
	)

AB – Add Binary (opcode 0xFE).

Adds the binary integer at [b_addr-b_len+1..b_addr] to the binary integer at [a_addr-a_len+1..a_addr]. Result stored in the first operand field. Second operand is not modified.

Parameters

ge	Emulator state
a_addr	Address of the rightmost byte of the first (destination) operand
a_len	Length of the first operand in bytes (1..16)
b_addr	Address of the rightmost byte of the second (source) operand
b_len	Length of the second operand in bytes (1..16)

Definition at line 68 of file alu_bin.c.

alu_ad()

void alu_ad	(	struct ge *	ge,
		uint16_t	a_addr,
		uint8_t	a_len,
		uint16_t	b_addr,
		uint8_t	b_len
	)

AD – Add Decimal (opcode 0xFA).

Adds two unsigned, unpacked (zoned) decimal fields right-to-left. Zones are ignored during the arithmetic. Result stored in the first operand field (zones of the result positions are set to 0x00 per the "zones not processed" rule; the caller / CPU sequencer is responsible for zone restoration if required).

Carry beyond the field boundary is silently dropped. Second operand is not modified.

Definition at line 200 of file alu_bin.c.

alu_sb()

void alu_sb	(	struct ge *	ge,
		uint16_t	a_addr,
		uint8_t	a_len,
		uint16_t	b_addr,
		uint8_t	b_len
	)

SB – Subtract Binary (opcode 0xFF).

Subtracts the second operand from the first operand; result stored in the first operand field. If the mathematical result is negative it is stored in two's-complement form (complemented to 2^(8*a_len)). Second operand is not modified.

Definition at line 118 of file alu_bin.c.

alu_sd()

void alu_sd	(	struct ge *	ge,
		uint16_t	a_addr,
		uint8_t	a_len,
		uint16_t	b_addr,
		uint8_t	b_len
	)

SD – Subtract Decimal (opcode 0xFB).

Subtracts the second unpacked decimal field from the first. If a borrow propagates beyond the most-significant position the result wraps modulo 10^a_len (consistent with the manual's description of unsigned positive integers with no sign handling in AD/SD).

Note: the manual states operands are treated as positive integers; the handling of underflow (borrow beyond the field) is not explicitly described for SD in the available OCR text. The implementation wraps modulo 10^L1 and sets cc=1 (non-zero) on underflow; this should be verified against page images. Second operand is not modified.

Definition at line 249 of file alu_bin.c.

dec_digit()

static uint8_t dec_digit ( const struct ge *  ge, uint16_t  base_addr, uint8_t  len, uint8_t  pos  )

inlinestatic

Definition at line 185 of file alu_bin.c.

field_byte()

static uint8_t field_byte ( const struct ge *  ge, uint16_t  base_addr, uint8_t  len, uint8_t  pos  )

inlinestatic

Read one byte from a multi-byte big-endian field at position pos (0 = least-significant byte = rightmost, len-1 = most-significant).

The field is stored big-endian in memory: MSB at address (base_addr - len + 1), LSB at address base_addr. So byte at position pos from LSB is at address (base_addr - pos).

Definition at line 39 of file alu_bin.c.

field_byte_set()

static void field_byte_set ( struct ge *  ge, uint16_t  base_addr, uint8_t  len, uint8_t  pos, uint8_t  val  )

inlinestatic

Write one byte into a multi-byte big-endian field.

Definition at line 51 of file alu_bin.c.